Why limited capacity for USB plug-ins on HUs?

[atomic punk]

Regarding this JVC KD-AVX33 head unit, specifically, but others in general:

Why does the manufacturer place a storage limit on the size of the plug-in USB device? Is it because the USB jack can only power smaller devices? I'd love to plug in my 250gb HDD to a head unit like that one, of course externally powering it with a 12/110 voltage converter to make the drive run. Is that even possible? Just curious. I talked to a couple tech help people from different manufacturers and they couldn't answer me.

Thanks.

 

[nserpa9248]

From what ive been told, the unit (the JVC) needs to at first scan the whole thing, etc etc. Then needs to constantly go back and forth in the flash drive for data.

Bigger flash drive, more time, more time, slower user interface, slower user interface, angry customers.

250GB would be nice, but the unit would prob be ridiculously slow...