This is a great idea in theory and I'd love it if it actually happened, but I don't see any practical way this could be implemented.
How would BeerSmith know which online sites to look at for prices? There are hundreds (thousands?) in the US alone. Just providing a URL to which site you want BeerSmith to look at wouldn't be enough.
How would it provide prices if you have more than one store available in your area and you're wanting to compare prices?
How would it retrieve those prices unless every homebrew store in the world agreed to provide prices in a specific database or format that BeerSmith could read? Some web sites list their prices in a table, some list them only on an individual page for each specific ingredient, some list their prices in a basic text layout. There's no way BeerSmith could read all the possible formats currently used by homebrew web sites.
BeerSmith would have to become a dominant enough software package, probably even used by commercial or craft breweries, before homebrew stores would be willing to agree to provide data in a standardized format.
It's a nice wish, though.