Probably 75% or so of Dell's business is in government and large corporation mass sales of identical workstations that will be configured/managed over a network. Don't need floppies for those stations.
Also, w/the price drop and subsequent proliferation of CDRWs (most new Dells come w/one) floppies are really not vital/viable anymore.
That said, they cost $10 are are nice to have for those odd times that you need them. They don't take up a normal IDE channel, and it's not liek you can put any other device on the floppy channel anyway (LS120s aside here) I mean IDE HDs/DVD/etc.