some people aren't thinking this out, how do you think oblivion would of been if you didn't have respwanws? or fallout 3?, so basically as the game moves along you would be in a more and more desolate map, is that really the point of the game?
If you CHOOOSE to make that the point of the game, then yeah.
to have fewer and fewer enemies to kill as you level up, so you're at level 25 with cool power armor or other cool gear and all these nice weapons but hardly anything left to kill?
And I'm telling you that you underestimate things. Look, aside from named NPCs, there's also numberous unnamed NPCs and various critters, so even if the game only spawened'em all at once, it'd still be by far enough for our XP needs. Besides, it's not like killing people are the only source of XP, as ypou seem to have forogtten. There's also doing quests - don't tell me that you only kill people for XP, never doing any quests? And then there's lockpicking and hacking, not to mention the miniquests of bringing various people stuff like scrap metal, books and so forth which rewards you with XP... I tell you, even if we went around killing everything or almost everything that moves, it'd still be plenty enough to satisfy any XP needs, I'd say.