never played SWG, but in UO, you COULD just go an fight dragons day 1 if you wanted. You'd probably die, sure, but you could. You could equip Platemail if you wanted. You probably wouldn't be able to move, but you could.
Same thing in SWG, if you had the cash to obtain said armor and could afford the shuttle trip to Dathomir, you could go out there and fight Rancors, etc. You would be 1-shotted, and probably not deal any damage, but you could.
There was experience, but it was specific to what you were doing. Use a rifle to kill something? Rifle XP. Then you could apply that to how you wanted to specialize your rifle abilities through 1 of 3 trees of progression. Healing yourself? That's First Aid XP, etc.
Again, this makes zones dependant on level, it's just obfuscated because you don't have a level requirement for entry, nor levels displayed to tell you if you are ready to go fight there or not.
My big complaints about the direction of MMOs all come from artificial/gamey restrictions and devices.
Want to wear this armor/wield this weapon? Nope, it's "bound" to so-and-so, because he's used it once.
Instancing is another evil here. It can be good, if implemented sparingly (again, I tend to prefer the SWG implementation here, but DAOC's wasn't too bad). Mainly when you make the highest level content only exist in an instance that only allows X number of people in (where X is small), then it reduces how epic the encounter feels.
Stat inflation is another problem. DAOC had a good way of handling this with implementing stat bonus caps. SWG had a good way of limiting item stat influence by restricting it to the crafters. Many people I talk to that get disillusioned with the WOW raid-treadmill is because a new expansion will come out and render every piece of equipment obsolete instantly.
Oh, and we need developers to stop making whole-sale changes to the underlying combat engine after release. SWG did it (twice). I was really disillusioned with LOTRO when they did it with their first expansion. Really? You didn't plan past the original release and level to 50? This was supposed to be a game that expanded all the way to Mordor. We didn't even get past the Misty Mountains at launch and they didn't plan well enough for expansion.