I'd go for something like this. At those prices and the handiness of being able to quickly find out what OC settings I need for GTA4 and what settings I need for Crysis 2 or what tweaks I can make for excatly my system in one location sounds good. However, if it wasn't that I'd be pissed. If I got a machine only to be told "these are the settings for this graphics card, adjust for your own accordingly", I wouldn't be a returning customer.
It does sound like a lot of work however and not something I could see a company accomplishing, but I've obviously not looked at any logistics to it other than thinking, there's going to be hundreds of combinations of hardware out there. There's hundreds of packages of software. How can you test them all?
Don't forget that for Macs, it's a limited field. There's pretty much one type of hardware and you don't get nearly as much software. Everything that's on Mac through their store is approved before it hits the user. There's a very limited number of variables.
Now how is one company going to be able to provide the same level of "hassle free" with say, every game on Steam?