Yes, all receivers do drop passes but not all at the rate that Owens does.
A case in point is that last year in 7 games he had 5 dropped passes. Terry Glenn also dropped 5 passes but that was over 16 games.
http://sports.iwon.com/nfl/stats/league/passesdropped.html
I no longer have access to the stats from previous years but every year I compare players and Owens has been routinely near the top in number and percentage of dropped passes.
He simply drops more passes than the other top WRs which drops him in my ratings.
As for Rice, this will come a shock to some here but I don't consider him the best WR ever to play.
Paul Warfield is the best WR I ever saw but he didn't play as long or have as many passes thrown to him as Rice. If he had it would be no contest, he would blow Rice's numbers out of the water.
That is not to say that Rice isn't a great player, one of the greatest of all-time, but I don't rank him as the best WR ever.