Actually, I misread the domain... I thought it was "mp3 hp", not "mp3 php"
I still believe that mp3 is trademarked, though I could be wrong on that as well.
Even so, I still don't see the value.
As for my domains and their prices, I focus on a niche market, and don't expect the general public to pay my prices. At $7/year, I'd rather sit on a quality generic domain in my niche, and wait for my industry marketing efforts to come up with the right buyer. I can tell you that I have sold many domains for those kinds of prices by focusing on my niche.