If it is turning over strongly, then it can only be one of three things - fuel supply, air supply, or correctly timed and sufficiently strong sparks from the ignition system.
I guess it could be a temperature sensor as you have already surmised, as if it doesn't know whether the engine is hot or cold this might making starting harder. It won't necessarily need to set a higher tickover and richer mixture when trying to start from cold in the summer as it shouldn't need much help when it is warm outside. I know my NC had very apparent higher tickover when cold, to the extent that