I would agree with your findings. Most Marriotts have the lounge open (with room card). I have seen pretzels or bowl of fruit. If they have a mini fridge - then that is open with water/soda. Usually the main fridge in the back is the beer/wine/milk - so that is locked in the kitchen.

I am usually away (work) during the day - but if Mrs. MSP Flyer comes with -- or it is vacation - we might stop in during the day. I don't recall any of them ever being locked during 10a-5p (but again - rarely am in hotel during these hours).

Personally - I always recommend taking 1-2 soda/waters from the lounge at night. Then I have these available during the day in my room (warm - but with ice it is ok).