It's "a better bargain" because:
1. Driver limitations make it less user friendly:
AnandTech warns us about ATi drivers for about the 4th time
In spite of the potential advantages offered by the Radeon 4870 X2, we have qualms about recommending it based on our experiences since October with the introduction of Core i7 and X58 and the multitude of software titles that were released. Driver support just isn't what it needs to be to really get behind an AMD single card dual-GPU solution right now.
The OP isn't using an x58... isn't that where the problems are that AT is talking about? It's not hard to find articles discussing driver problems with both companies if you search. AMD isn't the only current graphics maker that has any bugs in their drivers. Wasn't Nvidia actually named in a lawsuit over driver problems in Vista?
2. The 4870X2 doesn't offer the performance of the GTX295:
Comparing NVIDIA to AMD, it's clear that NVIDIA has recaptured the halo product at least in the majority of tests we ran in this snapshot of performance.
I'd say overall the GTX295 is a hair faster. But I don't think it's nearly $100 faster. And the benches I saw show the 4870x2 generally faster with AA, perticulary 8x. The GTX295 sure did clean up at 1280x1024 1xAA/1xAF though.

But I would imagine it's a toss up at resolutions and setting people will actually use this level of card at. What you get left with is two cards that are very, very near each other in performance, but one costs $100 more.
3. The 4870X2 has no good stereo 3d options.
I'm not sure I'd call Nvidia's 3d 'good' either.

Seeing as the OP would have to buy $200 glasses (I assume, he didn't mention he had these), ditch his 24" monitor for a 22" monitor (even if the gaming in 3d makes up for it, you're still stuck with a smaler, lower res monitor for everything else you do like internet, movies, etc. And if you go dual monitor with the 22" and 24" then while you'll have the 24" for everything else you don't get to sell it to off set the costs of the new 22"... trade offs I guess) and don't essentially you get half the frame rate using the 3d? Certainly it's not a bad option if that's something that really interests you, but I know for me I'm not even mildly interested until the cost of entry comes down.
4. The 4870X2 offers no hardware accelerated physics.
Nvidia offers no DX10.1 support. Both cards have some unique features. I think it's pretty one sided of you to point out just what Nvidia offers without pointing out any of the unique features that AMD provides.
5. ATi's Open CL solution has been pretty much going nowhere from what I can tell, but CUDA has gained a lot of momentum. For most of us, that means the opportunity for much faster transcoding of video.
I have no experience with this and am not too informed on it so I can't really comment.
The AMD part is priced where it might sell. it's the high end solution for people willing to trade $100 for it's limitations.
Yea, you get 95% of the performance overall for less then 80% of the price of the GTX295.