Maybe all software developers don't do it this way, but technically 0.21 to 0.22 IS a 0.1 increase. Version numbers don't work like normal decimals - 0.22 actually should be read as 22nd sub version. If it wasn't done this way, you would run into a problem if you got to 0.9 and made a 0.1 increment.
But your point is still a good one - if this is a major change, lets call a spade a spade and make this version 1.0. Now, I know that will attract the wolves - FOSS developers have a habit of holding their major version numbers at 0 to indicate they are in beta (seemingly forever).