If MS switches to GDDR5 now, did Sony make a silly mistake?

[yo_john117]

Question: Why doesn't MS just have 16Gb of DDR3 I'm assuming they'd still only need two slots (2 x 8Gb ram) and it would still probably be cheaper than 8Gb of GDDR5. The other question I have is would 16Gb of DDR3 be better than 8Gb of GDDR5 ram?