Why

[victor]

When I try to write the letter w it often changes to an s

[miasmum]

Fat fingers?

[victor]

Nope. Using a stick thingy that has a rubber bit on the end

[Suff]

The keyboard is trying to calculate what you hit on the screen. If your rubber bit on the end hits it exactly square on, then it will not try to determine what the letter was you pressed. But if it is a few pixels either side, it starts trying to work out if you actually meant to press another letter.

They learn over time.