Haven't looked at the tool but judging by the replies it's probably like most of these other online things.... maybe OK for less experienced users, but for seasoned PC gamers like many on this forum not all that useful.
In my opinion minimum/recommended specs are much less important than they used to be anyway, because nowadays 'everyone' has a 3d accelerator card... ok so the odd game might require dx8 hardware (ruling out e.g. gf4mx) but in general most modernish PCs, even those bought on the high street will at least run games, albeit with poor performance.
As far as performance goes, the way I do things is to completely ignore the minimum specs, look at the recommend ones, add 50% speed and that gives an idea of what kind of system you need for decent performance and visuals. So for example, BF2 recommends 2.4ghz, 1gig RAM, 256meg vid card. I'd say 3500+, 1.5gig RAM, and a 6800GT or better. Far Cry says 2ghz, 512meg, 128meg card; I say 3000+, 768meg, 6800 or better.
It's all a bit subjective as different people have different tolerances of framerates anyway.