You're correct. AFAIK all those pot shops in Colorado for instance are cash based only. And have vaults built to store all their cash because the banks won't touch it. There was an episode on Vice TV that touched on this I believe.
There was an amusing tidbit in CNN's High Profits (I think it was) where the Colorado tax department was having to put on extra security because the pot shops were having to pay their taxes by physically handing over bags of cash.
When legalization gets to my state I hope I have the foresight to have the planning and financing in place to be the first dispensary to open here.
These things are just redonculous cash cows.