This is pretty simple, I noticed that whenever I have Spotify streaming through a Bluetooth connection (phone / tablet), gapless playback works about 25% of the time, maybe less.
It's completely random when it works. For example:
If I hear a gap between songs in a gapless album (basically anything from Armin Van Buuren), I can go back and listen to the same two songs again and (sometimes) the gap won't be there.
I would imagine that a very large portion of the Spotify user base is using at least one Bluetooth device by now, and it only makes sense to add full funcionality for these users. I've been using Bluetooth streaming for headphones and my car for about two years now, and this is the one feature that just kills the listening experience when going wireless.
Please add gapless Bluetooth streaming support!
On a side note, this would go really great with gapless support for local files, but lets at least get the streaming side of things patched up!