Unpublished and unsolicited

I love and highly respect the written word, and do what I can to honour it -- be it by reading voraciously or writing copiously. Hence the diary and the two blogs I'm occasionally part of, but it has never been enough for me. I am a frequent slave of a mercurial Muse as well, that comes and goes at its leisure. Sometimes I don't hear from my Muse for months, and then suddenly it shows up and I'm stuck to my laptop or to a pad of paper and hard at work scribbling. I decided when I was eight to become a writer, and have been a slave to my infuriating Muse ever since. I started in Fantasy but have gradually gone into regular fiction. I guess I will always have a soft spot for Fantasy, as I have quite a few books of this genre on my shelf. I wrote out a trilogy when I was in my teens that would have probably gone down okay in the bookstores (pre-Harry Potter). It did not get beyond a couple of polite rejection letters. I revised it until I was sick of looking at it, and it went nowhere after that.
I had a dry spell for a bit, then moved to Mystery. The premise was good, or so I thought. (An actual published author thought otherwise, but he's a whiner, so the point is moot.) I still think the premise was good, only I lost interest in continuing with that. At this point, I am working on two projects, both fiction, and both look promising. Rest assured, I will perservere. My Muse is with me once again, and I cannot ignore its lure.
The thing I wanted to complain about is the phrase 'no unsolicited manuscripts'. This phrase ticks me off to no end. Publishing houses are supposedly on the lookout for new and exciting material. Okay, so why then do they say 'no unsolicited manuscripts'? This is a source of unending frustration. Perhaps I do not understand what they mean, but based on my understanding of 'unsolicited', wouldn't new manuscripts count as this? If you solicit materials, you are asking for them. Anyway, I am a little peeved about this phrase. If there is anyone out there who can explain the situation to me a little better, I would be grateful. Otherwise, publishing houses who add 'no unsolicited manuscripts' can go to the Devil.