Oops, right. 0.45 would mean version zero fortyfive, while 0.4.5 means zero four five. 0.45 would be a much later version than 0.4, and 0.4.5 means that it's a fifth (actually forth) bug-fix release for release 0.4. That nomenclature is mainly used on Macs, where the version numbering goes like this:
major . minor . bugfix
A change in Major means big new features.
A change in Minor means new or changes in features
A change in Bugfix means same features, just less bugs
Oh, and a 0 point something version usually means: "not ready at all yet". The first "normal" should always be 1.0.
HTH