With the new expansion, Eve servers are supposed to be able to handle huge fleet battles now, but yeah for the most part, all you'll see is blue/red boxes on your screen as you zoom waaay back. While you may be fighting 500 other players, it doesn't quite have the feel of say when Alterac Valley first came out in WoW or when global pvp raids went on.

Yea but difference is that those 20-40k players are in the same world/universe, unlike in diablo where you can have ONLY 8 players in same game.

Have you ever been in an alliance where you participate in operations of that size? I kinda doubt so. When theres hundreds and hundreds of people, real people, working together for a goal, you can't compare that to a few WoW kids running around on screen. Eye candy or not (And I suspect decent machines can handle close up views of those fights, mine can't cause it's old and crap, but I suspect anything half-way decent can). Plus I suspect you haven't partcipated in stuff that size because you turn off your color indicators on-screen and a ton of other vissual and audio settings to reduce client lag, not everyone has high enough computer to run it, so by rule those are disabled for fleet engagements across the board.

The StacklessIO and 64 bit servers can handle ~700 fighting at once on the "normal" nodes and about 1700 at once on the "hardened" nodes, like what Jita runs on. If you anticipate a battle large enough to crash regular nodes (700 people) then you can petition the day before and have the system put on a hardened node, and battles that size, alliance leaders know in advance to give them time to do this.