If clams are official currency in Woodland Valley, then when Pip and Pop ask for tons and tons of clams from Santa Hogg for Christmas, isn't that the same as saying "Give me tons and tons of money"?
Remember that they're kids. Some kids have written to Santa asking for money.
Clams are also Pip and Pop's Trademark Favourite Food; it's more like saying "Give me tons and tons of money ... that I can eat". Also, the show seems to distinguish between Woodland Valley Clams and actual clams: according to Muppet Wiki, the episode that introduces clams as currency shows the otters make two clams by selling ... clams.