Well, it depends on the type of data you send.
You see, 1's are slim enough, 0's are rather fat and may get slowed down by friction in the tinier electronic pipes.
As long as you send lots of 1's everything seems normal but when you want to actually 00 out a stick, it will get SLOW.
Though for very different reasons, the effect is not completely unlike what happens with cable connections:
though if you use 0's and 8's on those tiny USB sticks, you will actually worsen the issue