In real life, tripping an opponent makes him extremely vulnerable to getting kicked and trampled (by just about anyone nearby) or stabbed (by anyone with spear), while making it almost impossible for him to attack (except to kick near his feet) until he gets up.
A spectacular trip can actually be a high-amplitude throw, knocking the wind out him, breaking bones, knocking him out, or even killing him. The amount of damage is highly random, but a hard surface helps.
A takedown resembles a trip, but the attacker follows his opponent to the ground, gaining control, from which he can "ride" and wear down his opponent, go for a choke or joint lock, or stab through a chink in his opponent's armor with a dagger (misericorde). This leaves the attacker vulnerable to his opponents' allies though.
Then there's the larger point that a trip or takedown doesn't just succeed or fail; defense typically means a sprawl or a clinch, often with plenty of shifting.
And an attempt to move an opponent, like a bull rush, can easily knock him down.
Uh, yeah. I competed in wrestling in high school; you don't need to sell me on the advantages of knocking your opponent down or grappling with him.
So you are looking for a mechanical advantage - which is where the use of powers comes in. If you get a mechanical advantage out of it, it's a power. The amount of times per day you get a mechanical advantage out of use of a power is proportional to how powerful that mechanical advantage is.
Like I said in my previous post, you can trip, knockdown, etc your opponent until the cows come home if you like. But only under certain circumstances can you or your allies then
take advantage of having done so before your opponent can recover from the disadvantaged position. Since getting up does not provoke an attack (barring a power's specificity overriding the generality of Standing Up does not Provoke an OA), it doesn't break the Disbelief Suspenders that a basic attack described as a knock-down followed by the target springing back up doesn't provoke.
You're asking that a trip attack generate a mechanical advantage
each time it's performed, and that this be a Basic Attack. That just doesn't work in the 4E philosophy. Basic Attacks are just that, basic. And for game balance, a power that grants the mechanical advantage of applying the Prone condition to an opponent for a round is apparently considered overpowering by game design for an at-will power (I can't find another at-will power that grants all allies Combat Advantage against an enemy on a quick read-through, at any rate).
Some attacks described as tripping could be push, pull, or slides mechanically as well - opening up more powers to be used as trips.
I am seeing that if you insist on a 1:1 correspondence between mechanics and description in 4E combat, you will be disappointed. It's not built that way. Description of actions may or may not tell you what rule was used to generate it (a charging shield bash could be the description of about a half-a-dozen powers or even a basic attack) or what the mechanical effect will be (depending on the power used, the target could be pushed, slid, damaged, or have a condition applied). So a player saying "Gobsmack the brawler attempts to knock down his opponent" has no mechanical meaning. Is he using a basic attack, Tide of Iron, Covering Attack, Spinning Sweep, Steel Serpent Strike, Dance of Steel, Dizzying Blow, Griffon's Wrath, Shift the Battlefield, Thicket of Blades, Talon of the Roc, Warrior's Challenge, or a non-fighter power.
Tide of Iron is a very good one for this, actually - it's an at-will power that attempts to knock your opponent around. In some circumstances (where the opponent can't retreat to maintain his footing), you can actually make your opponent Prone till his next action. That's mechanics. Descriptively, you might have pushed him back hard enough to make him stumble, or even go to a knee or do a somersault, but he's not down for the roughly 6 seconds a round takes.
Spinning Sweep is an Encounter power, true, but all that means is that when you attempt the move, you may not have knocked the opponent down for long enough for it to matter. Sure, you tripped him or what-have-you, but he rolled with the blow and sprung right back up before you could follow up.
In short, anyone can trip at any time, but if circumstances don't favor it, the opponent can recover before he is mechanically disadvantaged. The trip attack did HP damage (as almost all attacks do), indicating that it used up some of the target's short-term burst endurance (and may have done some minor physical damage), but the target scrambled back to their feet/rolled with the blow/etc. Some people have extensive training in keeping the opponent down, and can lay them out for a couple of seconds before they recover their equilibrium.
