If you have a keyboard where "asd" is next to each other, would you consider "aSd" to be next to each other? Or "aS^D"?

And what about "edc" on a standard US keyboard? IMO, it doesn't make sense to disallow three keys in a horizontal row, but allow them vertically.

But then, what are you going to do on a keyboard that only has a few keys...? (An example of a keyboard that has only a few keys is a cell phone).