Can't blame ppl for wanting bigger. Yes, you probably could squeeze in a i7-2600 and gtx970 on a 450w, I know it's been done before. But running that close to maximum output by the psu for any length of time does have its own quirks. First, there's no guarantee that any particular buyer is going to get a high quality, tier 1 or tier 2 psu that'll withstand that abuse, many opt for more budget oriented tier 3 mediocre units. So quality power outputs, ripple suppression etc is dubious at best at closer to 100% loads. Second is the best efficiency, power to heat ratios, power cleanliness, fan noise, etc. is found in the 50% to 70% range. This is why any system running a gtx970 should be at a minimum of 520-550w. Third, there are no quality 500,600,700w units. None. For any quality unit you are looking at 450,520,550,620,650,750w units. So again, 520-550w is perfect for a 970. Forth is OC. This varies per user, personally my 3570k is at 4.3GHz and it's gtx660ti is max OC on a Seasonic M12-II 520w. My 3770k is currently at 4.6GHz (was 4.9GHz) and its gtx970 is max OC on a Evga G2 550w. Neither is overkill powered, but both are quality units designed to handle whatever I can throw at them and still come out smiling.
There's only one hard and fast rule of psus. Don't skimp. Be surprised how many people try and cheat that, only to end up with power related issues.