Look at Amazon instances. High-Memory Quadruple Extra Large DB = 68GB RAM!

It really depends on what your use case is.

Heavy reads and a large database? You are going to need RAM for your buffer pool.

Mainly writes and serving up reference data? Memory isn't such an issue.

We use Enterprise features (compression, partitioning, resource governor etc) but with very few exceptions our instances come well below the 64GB RAM. Part of that is because most of the estate is virtualised.