^ Yes...
And as for the concern on the graphic cards, by the time you would require more powerful setup than a GTX 275 SLI, newer cards would be available and you can just change to them instead of adding one more in Tri- SLI...And also more than 2 cards wont scale very well in many games...
But if you ask me I wont suggest buying 2 cards now...First off get a single GTX 275, check out its performance...they are good enough for a 1920X1200 resolution monitor(Though some games wont max out, but surely would be playable)...Save the money as ATI is set to launch newer DirectX 11 cards by this October and maybe you could get a more powerful graphics card for the current price of a GTX 275...
But if the newer cards don't have the significant performance gains, then later add one more GTX 275 in SLI...
And some info that you would have to know about Multiple card configurations...
Even adding 2 cards in SLI/ Crossfire configuration, it wont necessarily perform well...It depends on the game and the drivers...So in games, that dont support multiple card config, there wont be any performance advantage...Eg: Wow doesnt support multiple card config...
And 2 cards in SLI/ Crossfire would increase the performance say from 100%(Single card) to say ~ 140%(Multiple cards), maybe be little higher if the games have a very good support for multiple cards...