For the most part tablets will be relying strictly on integrated graphics to keep heat, weight, thickness and battery drain down.
Convertible / hybrid laptops will rely mostly on integrated graphics as well, but larger ones may allow for a lower performance dedicated graphics chip.
8" Windows 8 tablets will be relying on the Bay Trail generation Atom CPU which has lower performance and power consumption compared to the Haswell generation CPUs found in laptops. They are also limited to the 32-bit version of Win 8 and only 2 GB of RAM for now.