There might actually be some validity in that, since NiMh cells put out about 1.2v which is too low for some gear to work well.
The problem I always find with NiMh though, is increasing internal resistance after a few recharge cycles. It's usually not so much a question of o/c voltage alone, but that once the cell gets a bit tired the already marginal 1.2v drops to less than 1v under load. In that case trying to step-up the output will actually make things worse, not better.
I try to use lithium wherever possible these days. I know there are fire safety issues but hey, they perform so much better. In the case of lithium it's more likely the voltage is too high for equipment designed for alkalines, though. A batteriser to drop 3.7v down to 1.5 would be real handy, making lithium retrofit easy. Not likely to be a consumer product though, too much risk of costly or dangerous mistakes.