Cost - yes. The CPU in those consoles is laughable and the GPUs are also on the lower end - it won't be long before you'll be able to build a $700 PC that will smoke consoles and you don't have to pay for access to the multiplayer component.
Cost - No.
You're not building a PC with comparable specs, closed box environment, with a controller and headset packed in for $399, and you won't for many years.
Convenience - yes. Instant access to several hundred games spanning two decades
Convenience - No.
Games play instantly and download in the background, couch gaming, background patching, inevitable Gaikai streaming of the playstation catalogue.
Ease of use - it's not any more difficult to launch a PC game than it is to launch a console game. Add loading times that are MUCH quicker on PC and you have a winner.
See points above -- PS4 seems to be designed with ease of use in mind, even moreso than PC.
Bigger active userbase - YES. It will take 5-6 years for consoles to catch up to PC which has over 50 million active gamers.
Console games sell many times over what PC games sell. It's not about "HOW MANY PEOPLE OWN A PC", it's "HOW MANY PEOPLE ARE PLAYING COD/BF/ETC"
So? You're still getting better performance in multiplatform games. $1000 GPUs? PS4-like GPU will be well below $200 by the time PS4 launches.
I'm still getting 1080p games on PS4. All of these new-generation titles will be developed with PS4/XB1 specs in mind.
Advantage is for the PC if 60fps in every game is a requirement (for me, it's not), or getting in excess of 1080p resolution.
This is a non-issue for me.
If developers actually made games with the top 1% of graphics cards in mind that truly take advantage of the extra specs in ways outside of easily scalable factors, I'd be more inclined to care.