Another problem is that many of the wallets are multi-platform, and that means using cross platform gui tools like gtk or java... which generally look significantly crappier than native applications.  I think what is likely to happen is that the cross platform backends (like bitcoind) will get native OS frontends that look and behave like native applications (or even better). 

Also, right now, since almost all the wallets are open source and free, there's not a lot of economic pressure on developers to make their wallets pretty.