Consoles tend to have about 1/4 to 1/16 as much memory as PCs of a similar age so 1GB to 2GB of memory would be expected of consoles released this generation. The reasons consoles tend to use less memory is they typically use higher cost memory that has much lower latency and higher bandwith than comparable PCs.
2GB of GDDR5 is what I would have expected from the Wii U, but I wouldn't be surprised if it was as low as 1GB