Depending on the price of the house, the seller may not care. The market in Ames is so absurd right now that they may feel confident they can find another buyer. Can you find another house you like?
It certainly doesn't hurt to ask - all part of the negotiations- but if that house is sub-$250k, you might not have a lot of leverage.
Edit: if it's over $500k then absolutely demand it. Not an expert by any stretch, but that seems to be where the market is right now based on what Ove seen.
It's between the figures you quoted. Being that what I find from friends/family and online is pretty much universal that the seller is responsible, I'm surprised I'm told we 'really can't ask'. If there's no risk, why not ask? If they say no they say no and its ~$1200-1500; it's not a roof or a foundation.
I'll talk with my realtor tomorrow and find out what the deal is.