I may have been slightly OTT on the distances for CDG (19miles) and Heathrow (17 miles), but I've flown in and out of those airports on numerous occasions, and have never taken a cab (or even thought about it) if I'm going to the centre of the city. They may only be twice as far from the centre as Glasgow Airport is, but in general the traffic makes even the worst Kingston Bridge tailbacks look like a Sunday afternoon in the 1930s.
It might have been different if this rail link did as at CDG and linked you to the rest of the country. When I went to see Scotland's humiliation against Morocco in Saint Etienne at France 98 I got a TGV directly from CDG - perfect! But that wasn't the plan here - even with Crossrail.
I live in Glasgow and use the airport regularly, but I would never dream of getting a train there, with or without there being a station at the airport. When this was being mooted I discussed it with various friends and colleagues and not one of them thought it was something that they would use.
And as to people coming to Glasgow from abroad, why wait for a train to take you to a train station where you would in most cases need to get then get a taxi to your destination, when you could just get a taxi directly from the airport? It would be faster, a lot less hassle, and unless you were on your own, almost certainly cheaper too.
I've no doubt that a rail extension would have given some benefits, but would it have justified the costs - no chance.
For me, recession or not, binning this completely flawed project has to be good news.