Destiny is set in the future. Why most of the weapons have a "recent" design? For a game like this I expect that most of the weapons have a futuristic design, like halo for example. Only some exotics have a cool and futuristic design.
Future designs are all based on what we what we currently have. Look at 50's scifi flicks with their ray gun technology. 20 years from now people will think future weapons will be different. That being said did you ever stop to think that future people are nostalgic and design weapons based on old designs? Devrim Kay is such a hipster it makes me laugh!