what it comes down to for Sony is whether or not the PS3 has broke even/became profitable yet. At the launch of the machine it cost them $600 to build the unit yet they were selling for around $400.
This sounds crazy but don't forget that Sony OWNS Blu-Ray! Any Blu-Ray disc printed anywhere (officially) they get a cut on the sale of it. So they sneakily got a Blu-Ray player into everyone's living room who bought a PS3, meaning they will recoup the losses that way, as well as the obvious online sales through PSN.
The release of the ultra slim version of the machine is usually closely followed by the new upgraded kit as well, PSOne & Ps2 both followed this model.