a lot of time laptop usb ports handle extra current on the usb differently than desktops.
Desktop computers have an relatively endless supply of power, as long as they're plugged in, and the supply is working (and the bills are paid
Laptops, most of the time are designed to be solely run off the battery, so extra current isnt always available. Plus, the cheaper the model, the more cutting corners have been made.
In different models of the same manufacturer (i have expierence with HP and Dell {even was Dell certified}) the lower end models usb ports seem to act more like a "unpowered usb hub", while the higher end model's usb ports acted more like powered usb hubs.
YMMV
