Sure, those aren't cities, but I don't think you've quite understood just how small Manea really is...............
But that was mostly a tongue in cheek comment (the stop is just 2 tpd each way, it doesn't really justify not being Intercity). What does, however, is the fact that it regularly stops at small towns. Your Intercity via Saltash, St Germans etc. only stops at those places after having traveled fast from Paddington - Reading - Taunton - Exeter - Plymouth (or whatever service pattern happened to exist at the time). It then runs as a slow train due to various factors such as line capacity etc, but still runs as an Intercity service for most of its route (distance wise).
The same happens with TGV trains in France, if you want to travel to Nice (SE France), your train will probably have gone:
Paris Gare de Lyon, Lyon, Valence TGV, Aix TGV, Marseilles SC, before travelling pretty slowly along Toulon, Les Arcs - Draguignan, St Raphael Valescure, Cannes, Antibes, Nice (along one of the slowest mainlines in France) - it takes almost as long to travel from Marseilles to Nice as it does from Paris to Marseilles (which is about 4 x the distance). You'd still call that a TGV and not just because it takes TGV stock, but because it runs as a TGV for most of its line by distance.
I'd say a good list of things which make an Intercity service intercity include but are not limited to:
Speed of Service
Stock Used (and modcons included with that stock)
Stopping Pattern
Destinations Served
If you ran an equivalent Paddington - Penzance service that called all stations Paddington - Reading - Taunton - Plymouth - Pencance, then that wouldn't be an intercity, even if it very inappropriately used HST stock.