For example: The 512 MB of an XBOX 360 is not the same as today's RAM. We're talking 700 MHz compared to more modern standards like 1333 MHz. Nearly twice the speed.
RAM works a little different than you understand. The highest supported RAM speed is 667mhz DDR3 on PC (skt 1156, core i7 chips). Because you carry data on the front and back of the signal, you carry 2 bits per cycle, so it's effectively the same speed as 1333mhz SDR.
GDDR3 is nothing to do with DDR3. Instead it's a high speed/high voltage part designed for graphics card well before DDR3 was around. But it also plays the same DDR speed trick.
DDR3 1333 has a peak bandwidth per module of 10.6 GB/s, dual channel puts that up to 21GB/s roughly
X360's 700mhz GDDR3 has a peak bandwidth of 5.6 GB/S. However it effectively runs in octo-channel, giving a peak bandwidth of 44.8 GB/s.
So if you're talking speed, the X360's RAM is way faster. However we've also got really fast RAM on our graphics cards, it's just the X360 uses that same RAM for system as well.
Don't underestimate the huge advantage of having one standardised system spec either. When you know exactly how much resource you have you can make full use of it, rather than having to either code for the lowest common denominator or code several versions of things to cater for different system builds.. which leaves less time over for optimisation etc.