Your experience with the Salks mirrors my own. They sounded very nice and tight without a sub in the room. I played them for about two weeks with no supporting sub. They have an excellent sound and as
@TLS Guy mentions, a goodly number of very fine setups are overbiased to bass and the overall sound is not what it could be.
Also as
@TLS Guy mentions, in a music system (the Salks are in a music only system) there really isn't all that much for a sub to do if your mains are up to snuff. Get out one of those nice graphs that show the frequency ranges of most instruments. It surprised me to see most musical instruments don't go anywhere near subwoofer strengths. And just because an instrument reaches the lower registers, it doesn't mean it does so with a lot of power.
I did eventually put a sub in with my Salks. I did so "just because I can" more than anything. But, I did like the authority it added to certain types of music. Mostly, you can't tell its even in the room. But, when the right source is played, it really puts some pop in the finished product. I like having the additional muscle, but, I also like having it setup so its not overbearing or coloring where it shouldn't.