The Munich Airport Marriott, which is actually about 15 minutes away in Freising, charges € 10 each way for shuttle service, which must be reserved ahead of time. Taxicabs are normally about € 25 each way. Both costs are shown on the website. I prepaid for shuttle service to return to MUC for an early morning flight. The shuttle turned out to be a taxicab, and there were no extra charges.
In another non-Starwood experience, I recently stayed at the Gulfport, MS Fairfield Inn. I selected this hotel by searching on the Marriott.com website for hotels near the GPT airport. The Fairfield comes up as 0.5 miles from the airport, so I assumed that it is an "airport" hotel with shuttle service. I was wrong -- they do not have shuttle service, and taxicabs charge a $10 flat rate. Not a big deal, but I now know not to assume free shuttle service even if the hotel is right on the edge of the airport. BTW, had I looked more closely at the information on the website, I would have seen that the estimated cab cost is shown.