Really, there aren't a lot of decent proprietary parts out there. Everything is SRAM, Shimano, or a compatible/clone/copy.

I would imagine that BikesDirect couldn't afford to use non-compatible parts anyway, because they buy in bulk, and wouldn't want a mix-n-match issue in the warehouse---half-pallets of stuff they couldn't use with the other half-pallets of stuff.

The only time I have run into oddball/irreplaceable parts are with ultra-cheap bikes where stuff gets stamped out of pot-metal or cast in cheap plastic (and they are usually compatible with other manufacturers parts, but cannot be purchased separately) or with regional oddities .... Italy had its own BB standard a few decades back, France used (if I recall) the same size but different threading, and for a while Raleigh used a size almost exactly the same as BSA but a tiny bit different.

As far as I know, all those little differences have gone away. There is still an idiotic array of BB standards but in most companies several companies make each size/style.