It's a parctice that dates back to 2006 when the API was first written, and frankly isn't covered by the coding conventions. Same thing with the docblocks, they're all copypasted with some bits changed and don't even make sense if you look at them in the genereated code docs.
I don't feel that any of us depend on this anymore (get a better IDE), so in the inerest of consistancy it's time we said goodbye to it.
Basically api was thinking qplimit was the offset, and qpoffset was the limit. Also remove an extra ! when checking for the cached timestamp which was stopping the display of cachedtimestamp property in the api output.
I'm going to tag this 1.18 since this module was introduced in 1.18, and I assume we'd want to fix the limit/offset parameter before the wrong behaviour gets released and people depend on it, etc.
