I would say it all depends on the motorbike.
Some are fine during the winter other aren't.
Example: I have to keep mine under cover as it's fuel injected with RAM air which means all the contacts need to have a quick squirt of WD40 and ignition advanced slightly, also 'cos I'm near the coast and the gritting trucks are out I have to ensure I give it a rince down to get rid of the salt.
With storage I would advise the following:
Remove battery terminals and put the batt on a slow trickle charge
Drain the feul tank
Rotate the wheels 20-40 degrees around every week to keep the presure points different
Change oil and clean the air filter before starting up again
Make sure the braking system is still sealed and the callipers aren't sticking
Plus the normall checks, tyre pressure, lubricant in the cable sheaths.
Having said the above, I have one bike which just needs a quick service once a year (used all year round). Unfortunatly the other bike is a b1tch to keep running sweet