In other words... (Score 2, Interesting)

Holy hell, this thing is gonna cost a lot to make! Cut costs! The downside is the same as for the PS2, if its not standard equipment, developers will assume that the majority don't have it and won't use the features. Tough decision for Sony, but in the long run at least the marketing folks can still say that it has hard drive capability to compete with MS, even if most games will ignore it.