One can find MPEG-2 TS in surprising places (see: DOCSIS encapsulating Ethernet frames into TS packets).
If I had to guess why MPEG-2 TS, it'd probably be the for the fact it's a well-supported streaming format in both hardware and software. If you tried using QuickTime or MPEG-4 containers, you'd have to rely on hacks like ensuring the moov atom preceeds mdat.
Matroska may be worth considering (especially the subset used by WebM to make it stream-friendly and quicker to seek), but no idea how widespread hardware support is for (de)muxing that.