well, a lot of dSLRs are simply 2:3 by nature, just as 4/3 format cameras are 3:4 by nature.
You do have some cameras Iand smartphone) that allow a choice of format aspect ratio, even when their inherent format is something else, like smartphones being 16:9 or so.
Don't forget that no matter how it was originally shot, EVERY time you choose a print size it is very likely to require a different aspect ratio...
4x6 differs from 5x7 differs from 8x10 differs from 11x14 differs from 13x19 differs from 14x17...and so on.
So if you sell your photos, the actual aspect ratio is going to be dependent upon the size of print that is desired by the buyer.