Actually, the real Terms and Conditions are, now at least, fairly specific in defining an Enhanced/Preferred room upgrade for Gold members:

4B.9 (b) An Enhanced/Preferred Room at Participating Properties at the time of check-in based upon room availability for your entire stay, except at Aloft and Element properties. Enhanced/Preferred Rooms are identified by each property and are restricted to the class of room originally booked, but may include rooms on higher floors, corner rooms, newly renovated rooms, or rooms with preferred views. The upgrade benefit is available for one room for the personal use of the Member only, regardless of the number of additional rooms purchased by the Member.

However, as it applies here, that doesn't mean the property wasn't guilty of fomenting a room type discrepancy issue if a studio room was reserved originally.

Best regards,

William R. Sanders
Online Guest Feedback Coordinator
Starwood Hotels & Resorts Worldwide

[email protected]