Yep, and those bond (and swap) prices are not public prices in the same way as equity prices from exchanges. They're indicative dealer quotes. ALLQ shows a stack of dealer quotes. No other system does this...
Eh, you're a bit off. You can find compiled quotes in lots of places, and individual quotes from any broker or dealer, so there are other systems that do this (maybe none that have exactly ALLQs same dealers giving quotes). But you're right saying that many times these prices are indicative quotes from dealers.