Not that I'm that deeply aquainted with trainer skewers, but from what I've seen they're just a bit chunkier at the end caps to allow more engagement for the trainer to clamp against. I left mine on for road use as well. Trainer tire isn't mandatory at all. I've used tires retired from road use on trainer until they've shredded. That works too. I'd only buy a trainer-specific tire if I had to buy a tire in the first place - in which case I might go for dirt-cheap tires from the department store instead...