ITH used to not be the US monopoly it is today. A NW agent told me that once upon a time, they came to Ithaca (but they left before I started using ITH in '94). Continental Express, with a lineup of about 4 prop flights to EWR, pulled out a few years ago, leaving the current monopoly. Fares tend to be higher for ITH relative to SYR (and on US, that means something).
It leads to the 'ol rural airport dilemma -- support your local home-town airport, getting you convenience and also increasing the passenger stats, making it more attractive for other carriers to serve your airport -- or fly out of the city, often times realizing substantial savings.
I would think that a carrier stronger in the Midwest and Rockies (anyone at Mesaba listening?) would pick up substantial business in ITH. Mesaba already flies Dash-8's to ELM and BGM; why not add ITH to the loop? Lots of reasons, I suppose, or they'd be here already.
Pity us small-town FTers who dream of Dash-8 service someday