So, lset's get the 'off topic' bit done first. Here's my explanation of why two CR x monsters aren't worth an EL of 2x. It's a matter of available resources. At a certian point, the power curve assumes you'll have particular resources. If you can overcome one creature with DR 5/+1, you'll probablly be able to overcome the second one as well using the same resources (in this case, let's say a magic weapon spell that will be active through an entire combat). The relationship between spells used, distances traveled, area effects, spell durations, magical weapons, monster abilities and available tactics is a large and complex web. And I'm thankful for the tools. In fact, I'm running Exalted now, and I greatly, greatly miss the CR system. The CR system is a wonderful tool, and I think that's why it's being defended so much.
Now, on to the topical discussion. Bad DM's aren't fun to play with. And, you know what? It's true. But, I've tended to find that bad GMing and poor players are actually related. Not necessarrally that bad GMs are a result of bad players, or that bad players are the result of bad GMs, but again, that the relationship between them is a system that feeds on itself. Good playing helps bring about Good GMing. Good GMing brings about good playing. Bad GMing brings about bad playing, and bad playing brings about bad GMing. Maybe 'influences' is a better word.
Depending on the game, sometimes encounters greater then the group's abilities are ok. I mean, if the level two party really does want to challenge the Queen's Champion, reknown dragon slaying knight, then so be it. However, for the most part, you are correct in that the typical range of encounters needs to be suitable for the party. Likewize, the treasure should, in most cases, be the assumed standard, flavored to taste.
Roleplay is contingient on the same Player-Dm interaction, also agreed. The players have to do so, and the DM has to let them/give them chances to.
Aside from the overstated initial opinion, I have to agree overall. Though I find it amusing that, by your examples, I am a great DM, when in fact I range from above average to poor. = ) Again, it's just never that simple.
Anyway, things I would say to anyone taking DMing 101:
Know what game you want to play. Have a good idea about what you want to do, and keep with it. Try and keep the tone going, and the themes going.
Reward your players when they do something right. It doesn't have to be a big reward, but if they follow the plot hook, or try talking to the queen, give them some sort of positive outcome, even if they fail. This is more of an early on rule, to establish that it's ok to take action. And it doesn't need to be loot. If they rescue a town, have the people be greatful, maybe let them stay free at the inn (as long as they don't cause trouble, and there isn't a rush for rooms). If they feel good about something, chances are that they'll try again.
Learn about your players. Find out what motivates them and what they enjoy, then play to/with that.
Talk with your players. I can't stress this one enough. If there's a problem, take some time and mention it. If you need something, say so.
Well, short of just linking to the DMing advice thread, anyone else have things to add?