PC games are usually not required to support low specced PCs, this measure limits the freedom for developers to develop their game according to the specifications they think is desireable for their game. GTA IV development is affected by the core's lack of a default harddrive and the XBox 360's DVD storage limitations. As this is a cross-platform game this will probably not only affect the XBox 360 version, but the PS3 version as well. So we may never know what Rockstar actually had in store for us.
IMO 2.5 inch harddrives aren't that expensive and for me would be well worth the extra bucks to have the harddrive neatly stored inside the PS3. But 60GB is more than enough for now, if at some point I will upgrade the harddrive I will probably go for a 200GB drive which will likely have gone down in price by that time.
