Winter storage

Even though I live on Vancouver Island, and could basically ride year-round, I've decided to park the Sprint for the winter. I've lots of experience storing a bike for the winter, but have been wondering lately...

Why do I need to replenish the oil when I drain out the old oil? I'm not riding it any where, and have no plans to fire her up. It has always had synthetic oil so the parts should be well protected since I believe synth oil stays on the metal parts much longer than dino oil.

Any thoughts about this??

Must say, I had an enjoyable time this year and look forward to '07!

Cheers.