You said:
I was just pointing out that, as usual, when your knowledge of 1e is comparable to my dog's knowledge of quantum physics. Try actually reading the books before spouting off infactual information, please.
At 1st level, any party with a ranger, elf, or halfling has a reasonably good chance of gaining surprise. Surprise indicates the other party is unaware of your presence, and you may withdraw with them being none the wiser. I.E, you do the scouts job. I'd say quite a lot of parties have at least one of the above class/races, so the chance in many cases is much higher than 15%.
You said that there was a 66% chance for the right kind of scout to surprise the monsters. That is unlikely to be true, but I am always one to look for further analysis.
Let's take a typical scenario: A lone elf vs. a generic monster. While it is true that the elf surprises the monster four times out of six, he is himself surprised two time out of six, and the partial surprise segments must be accounted for, too. Also, if a door must be opened, that drops the chances to dead even. In the dark, PCs without infravision (like most rangers and halflings) must generally carry light, potentially negating their ability to effectively scout.
The monster involved also changes this considerably, as several have their own surprise modifiers. Given that you may not know what monsters are present, or even with some foreknowledge, there may be some of which you are unaware, you could find your situations somewhat reversed, with the surprise advantage slipping to neutral or to team monster. (IIRC, there is a monster that has a 90% chance to surprise in generic situations, though I could be remembering something from 2nd Edition.)
Let's look at a couple generic situations:
Code:
Key:
M#: The number of segments the monster is surprised
E#: The number of segments the elf is surprised
R#: The number of segments the ranger is surprised
NS: No net surprise segments
monster roll 1 2 3 4 5 6 1 2 3 4 5 6
elf roll rgr roll
1 [COLOR="Yellow"]NS[/COLOR] [COLOR="Green"]M1 M2 M3[/COLOR] [COLOR="Red"]E1 E1[/COLOR] 1 [COLOR="Yellow"]NS[/COLOR] [COLOR="Green"]M1 M2[/COLOR] [color="Red"]R1 R1 R1[/color]
2 [color="Red"]E1[/color] [COLOR="Yellow"]NS[/color] [COLOR="Green"]M1 M2[/COLOR] [color="Red"]E2 E2[/color] 2 [COLOR="Green"]M1 M2 M3[/color] [COLOR="Yellow"]NS NS NS[/color]
3 [COLOR="Green"]M1 M2 M3 M4[/color] [COLOR="Yellow"]NS NS[/color] 3 [COLOR="Green"]M1 M2 M3[/color] [COLOR="Yellow"]NS NS NS[/color]
4 [COLOR="Green"]M1 M2 M3 M4[/color] [COLOR="Yellow"]NS NS[/color] 4 [COLOR="Green"]M1 M2 M3[/color] [COLOR="Yellow"]NS NS NS[/color]
5 [COLOR="Green"]M1 M2 M3 M4[/color] [COLOR="Yellow"]NS NS[/color] 5 [COLOR="Green"]M1 M2 M3[/color] [COLOR="Yellow"]NS NS NS[/color]
6 [COLOR="Green"]M1 M2 M3 M4[/color] [COLOR="Yellow"]NS NS[/color] 6 [COLOR="Green"]M1 M2 M3[/color] [COLOR="Yellow"]NS NS NS[/color]
For an elf, the monster is (net) surprised 58% of the time (21/36), the elf is surprised 14% of the time (5/36), and there is no net surprise 28% of the time (10/36). That is a bad situation (the scout or no one being surprised) 42% of the time. In order to gain even this benefit, the scout must be alone (or the whole party must be elves or whatnot). Assuming a lone scout, being essentially alone (or more than 90' in front of the party) can be a dangerous thing in a dungeon. 42% of the time, you are the only target available for the monsters to attack and do not have surprise on your side.
For a ranger, the numbers are less favorable in some ways, less penalizing in others: the monsters are surprised 47% of the time (17/36), the ranger is surprised only 8% of the time (3/36), and there is no surprise 44% of the time (16/36). Rangers can be surprised less (and only for one segment, ever), but they are at an advantage less than half of the time, and 53% of the time, they are facing the monsters as the sole target, either themselves surprised or left to the vagaries of initiative.
You also note something like "surprise means that the monsters are unaware of the party, so they can avoid the encounter if they so choose." That, however, is only one of the options for surprise. It is entirely likely that the DM chooses that the monsters are unprepared (or otherwise slow to react) instead of unaware. That means the surprising party can elect to flee or fight, but are not likely to completely avoid the monsters.
My own rubric for that would be whether or not the PC was surprised by the monsters. If the PC is surprised, the monsters noticed the scout, but were slow to react; if the monsters were the only ones to be surprised, then the PC can withdraw without notice. That puts rangers and elves able to "effectively" scout about 33% of the time. The rules have no guidance on that, though. A DM could just as easily rule that all surprise is reaction-time based, and never due to a party being unaware, or could leave it to chance (throw a d6: even, reaction time; odd, awareness). Like many other things in AD&D, the PCs ability to avoid encounters is largely left to DM fiat. Not that this is necessarily a bad thing.