Anyone running Windows instances on EC2 will tell you that a 30 GB EBS partition only gives you around 10 GB of usable space. Windows takes up a lot of space (15 GB for 32-bit and 20 GB for 64-bit) even before apps get involved.
I remember when the original iPhone debuted, I was completely SHOCKED that Apple was able to reduce the footprint of OS X so dramatically. A 8 GB phone still gave you 6.5 GB of free space. Then with the release of Snow Leopard, Apple more than halved the size of the space required to install OS X.