Developing for a PS2 is totally different from developing for a Game Cube or developing for an Xbox or developing for a PC or developing for a friggen SGI, Alpha or HP PA-RISC.
They're all completely different with the minor problem consoles used very closed and tight technology. You're better off spending all your time developing for one platform - and in this instance THQ obviously got some help from sony or had already purchased devkits for about ....$20,000 USD or however much it is now (plus that and they have to use Maya for GAMES dev work..bleurgh)
From a buisiness perspective it makes sense to use the resources you have rather than investing in a totally new pipeline.
IMO its better for them to develop on an open system to start with rather than a closed one, but since i'm not a clueless THQ exec i don't pull the strings.