On the one hand, with a PC you can always be on the cutting edge (or close to it) by upgrading your hardware as needed. If having the best hardware is important to you and money doesn't matter, then it makes a lot of sense.
With the PS3 (or PS4), you will never be able to upgrade it's hardware. That's the problem that console users face, if upgrading hardware is important to them.
The trade-off? A $500 PS3 will last 5-7 years. For those 5-7 years, games will continue to look good and play well. There is no gaming computer that costs $500 and will continue to perform well (without upgrades) for 5-7 years. It doesn't exist.
I'm speaking as someone who owns both a computer and a PS3. I love both systems, and I believe that different games are better on different platforms. Each platform has its own strengths. But that's not really the question here.
Computers eventually outpace platforms simply because they can be upgraded with new technology as it becomes available. Having said that, upgrading hardware on a regular basis isn't free.