When there is a component which is faster than another component there will always be bottleneck no matter what the situation is.
Rendering or even gaming both need higher end processors than the Core2 series. People don't throw away their PC's just because it's old or slow, they throw them out because they won't be able to upgrade to anything better or faster. Because by doing that, they have to upgrade their motherboard thus also their CPU and RAM, since most LGA 775 (Core2 socket) CPUs use DDR2 memory or even they did have DDR3, they will be limited to 1066 due to the limit of the chipset's front side bus.
You can get more expandability, cheaper price and far better performance, not mention reliability and the fact that you'll have something cutting edge new, for the same amount of money.
Now I don't see why should anyone waste money on something slow and old with the possibility of spending more money on upgrading it when they can directly get something newer and better and even cheaper for the same price.
But when it comes to the fact of buying something that costs cheaper and older but have the same socket and almost the same performance is something different. For example, I am building a very budget gaming machine for a friend and I'm using an H61 board instead of a B75 board (H61 is older) But due to the fact of H61 being cheaper and not effecting the performance and the user experience I don't see any reason to spend $90 more on a B75 motherboard when the user won't feel any difference.
Same story in the case of CPUs. Some people tend to buy older architecture CPUs to save a bit of money on something like a graphics card. But they do that because Intel has a "Tick Tock" strategy where the "Tock" has major architecture changes (Performance wise of course) and the "Tick" is just an architecture shrink (Like Sandy Bridge vs Sandy Bridge). In this case, buying an older architecture CPU will be far more cheaper and will have almost the same amount of performance.
Not to mention with today's new "i" series of processors being insanely cheaper and faster than Core2 processors. It doesn't matter any more whether to get the latest or the older architecture (This is in case of the "i" series). Because an old 2500K (Second generation i5) can still handle up to 3 or 4 high end graphics cards without having a hiccup where something like a Core2Quad can barely handle an old GTX460, due to bottleneck. And a GTX 460 is now too old of a card to give great performance in 1080P games, due to the fact that games and programs are keep getting more demanding. Max Payne 3's recommended requirements suggest you use a GTX 580 with a 3930K (A $600 processor) A 3930K scores 12089 in CPU mark whereas the Core2Quad 3GHz scores just 4,057 CPU mark points.
The Core2 Quad has the power of an i3 and costs double of an i3. The Pentium G850 @2.9GHz scored 2,662 where the Core2 Duo E8600 @3.11 GHz scored 2,406 CPU mark points. The Pentium costs 60~ish dollars and the Core2 Duo costs 280~ish dollars (At that time)
And don't let me get started on power consumption...
Look at it yourself @
http://www.cpubenchmark.net/
