Cheebee, first cartridges are 2 GB, not 4. Though it won't take long for them to grow well beyond 4 GB if needed.
Carts have that great feature of in cycle capacity increases. If you look at the cart sizes of all Nin consoles from launch to the biggest cart, a magnitude of 10 is common. DS cards have gone from 8 MB to 512 MB.
The rEVOLution is not being televised