There would be some massive practical problems with using airport-style security measures at inter-city stations. For example, the small station in the town where I live is unstaffed (as are quite a few stations along the route it lies upon), so body scanners wouldn't be practical here. However the stations at either end of the line are classed as 'inter-city', so I can catch a local train here and then arrive at an inter-city station (and hence board a mainline train to London) without the need to pass through the entrance area of an inter-city station. Knowing the layout of those major stations, I can't see anywhere that screening facilities for passengers arriving on local trains (rather than entering the station from the street) could be introduced.
Even where there are already security scans at mainline stations, they seem to be there as a 'confidence building measure' for the public, rather than being genuinely effective. Nearly 2000 people were killed or injured by the attacks on the Spanish train system in 2004, so it's probably unsurprising that there are long queues for the stringent security checks if you want to board an inter-city train at Madrid's Atocha station. However you can't even join those queues until you've passed through a packed concourse (which would be a target for a terrorist attack in itself) and there are no checks whatsoever on passengers boarding local trains or Metro services.