Just checked my copy of the Elite Members Guide.

Mine happens to labeled "Platinum" but the "Benefits At a Glance" table printed on the inner cover notes that Golds as well as Plats are entitled to the "Guaranteed Room Type" (There is an annotation that "Benefit varies by partcipating brand - Log on to Marriott Rewards.com for a complete list of Terms and Conditions"

Here's how it's addressed in the Terms and Conditions (note that Golds do have restrictions.:

5. The Room Type Guarantee covers bed type preferences at Marriott Hotels, Resorts & Suites and Renaissance Hotels, Resorts & Suites and smoking/non-smoking preferences at Marriott Hotels, Resorts & Suites, Renaissance Hotels, Resorts & Suites, Courtyard, Fairfield Inn & Suites, Residence Inn, SpringHill Suites and TownePlace Suites properties (pillow, room location, extra bed, crib requests, etc. are not included in the Guarantee). Exact bed sizes may vary at International hotels.


6. The Room Type Guarantee does not cover room upgrades.


7. A member who makes a reservation on the same day he/she plans to arrive at the hotel, or a member who walks in to a hotel without a reservation is not eligible to receive the Room Type Guarantee.


8. Platinum members are eligible to receive the Room Type Guarantee at any Marriott Hotels & Resorts, Renaissance Hotels & Resorts, Courtyard, Residence Inn, Fairfield Inn & Suite, SpringHill Suites or TownePlace Suites property worldwide. Gold members are eligible to receive the Room Type Guarantee at any Marriott Hotels & Resorts, Renaissance Hotels & Resorts, Courtyard by Marriott, Residence Inn, Fairfield Inn or Suite, SpringHill Suite or TownePlace Suite property located in North America.

Click on http://www.marriott.com/rewards/term...eliteguarantee for the (MR) screen upon which the above appears: