True, you can only view one source at a time, and this can be disturbing in some occasions, but well... like it's been said - one can always launch another editor
Yes, I like tabs also, but there are occasions of where tabs aren't appropiated, for example what if you want to see 5 files at the same time inside C::B (ie. 2 source code, 1 xml and 2 wxSmith resource windows). With tabbed interface it can't be done -at the same time-.
But regarding this, it's not THAT important in windows/linux, because any application do whatever they want. But on OS X the floating windows are the standard, and the users of that OS are used to that. Like they are used that a Maximize button doesn't exist. The entire concept maximizing doesn't exist, you can't maximize a window.
The functionality (and options to choose from tabbed, mdi, or floating) should come from the docking library or from wxWidgets.