There was an interview with a designer/artist at one point, and he was asked about the whole 1 weapon per class thing.
His response was, that every race is animated by hand, meaning its not an automated process like some games do, so in order to preserve the uniqueness (is that a word?) of the races and their animations they had to make sacrifices somewhere.
The argument was we can automate the process and it would look the same swinging an axe and a sword, or do what they do and make the animations for 1 weapon 'awesome'.
Don't know if I buy it to be honest, but it's not a huge deal for me in the first place, so whatever. Most of the skills have fancy animations anyway, so I could care less about weapon variety, as long as the 'skins' for them are different enough.