I think others have mentioned, although alder is very balanced and gorgeous tone, it's not terribly pretty and needs to be painted, so it costs less.. My best strat is alder.
And it's some have already mentioned, there are plenty of rules to be broken. My Parker nightfly is maple, it's a wee bit bright but a JB works great in it and it's not ridiculously heavy.
From my perspective, wood does have a significant impact on tone, however pickups have the most impact and the variations in any slab of wood can really mix up the final tone.