You're full of shit. If a cop pulls you over while you're smoking weed, its a DWI.
Now if you were to say that the cop let you go, that would be one thing. But if a cop were to write a report about it (like they gotta do with any violations, criminal or not), he would have to give you a DWI.
Otherwise, this cop goes back to the station, hands in his paperwork. When the shit gets processed they gonna be like "you caught a guy smoking weed while driving and only gave him a ticket?" *axe*
like I said, full of shit