I know.  Just how the PS3 formats the internal HDD so you can't put it back in your PC.

Right?

Yes, but on Ps3 you have 100+ GB of already avaliable space in the internl hard drive, you don't need another storage.

Their choice to pack WiiU with a cheap flash storage that can be later expanded with your HDD makes sense only if you can use any HDD you have in your house. If you have to format the file system, than it's no different than using a proprietary drive.

You're missing the point.   If you want to increase the storage capacity of your PS3, you have to purchase a 2.5" internal HDD and format it for your PS3.  It then becomes unreadable by your PC unless you reformat it back to NTSF or whatever you OS uses.  You can't just use any HDD in your house for the PS3 either.   It must be a 2.5" laptop style drive.

With Wii U, you can buy a complete external HDD or buy an external case and turn any HDD you want into an external HDD.

Yes, the built in storage is low but you compalained about the "closed storage system".  What I'm telling you is that the same thing happens with a PS3 stoage upgrade.

can u hook up a usb hard drive to the wiiu from day one??

My question exactly. I'd like to know if I could partition half of my external for this so I don't have to buy another external