I agree with you on that.
I have a CULV (SU7300) laptop. I put an SSD in it since the stock 5400 rpm harddrive is slow as crap. I easily get 10 hours on the battery, if I don't stress the processor too much.
But usually smaller and lower costs platforms come with a much weaker battery. When the difference at full load is x2 the effect on battery life could be much bigger than your example. And 1GHz is still too slow in by book, that should put it around a dual core Atom 330 performance wise, which is not that great.
One more thing to consider is cooling. I haven't really tried put a very long lasting load on the CPU in my laptop, but in normal usage, it runs very cool. When you double the power consumption, the heat output increases by leaps and bounds, so that's something worth thinking about. For example, I have a first gen eeePC, it's just a 630MHz Celeron M, but the power hungry chipset causes it to be unusable on the lap for long, it just gets too damn hot, if I had the option to cut the amount of power consumed by half or even a third, it'd probably wouldn't be too bad.