It is true that it varies by hotel. But generally, I would argue that any hotel will keep its top rooms/suites (specialty suites or rooms) to use only at its own discretion and not generally for any Platinum or SNA upgrade pool. We can disagree on this point, certainly. But my experience shows this to be almost universally true.

When a hotel has many suites, it’s just more likely that there are more categories of suites; namely, there are specialty suites normally unavailable for a Plat and SNA upgrades, and there are lower level suites and perhaps better category view rooms available for Plat and SNA upgrades.

When a hotel has few suites, it’s just more likely that those few suites are entirely part of the specialty suite group unavailable for Plat or SNA upgrades. The Plat and SNA upgrades in these hotels are more likely to be higher category/better view rooms rather than proper suites.

It’s all about likelihood—there can be a range, of course. Some hotels with fewer suites may be more generous AT THEIR DISCRETION. Some hotels with more suites may be more strict AT THEIR DISCRETION. That discretion will vary depending on the nature of the market, the hotel brand, and the average population of Platinum guests.

Few hotels overall make their best suites available for regular Plat and SNA upgrades. That’s perfectly appropriate IMO. But that being said, as both a SPG Plat100 Ambassador and as a Marriott Plat Premier with Ambassador, I’ve been upgraded to top level specialty suites on any number of occasions—almost always at hotels with a lot of suites, but even at hotels with just a few suites. And that’s why I’m such a fan of the Ambassador program, both before with SPG and now still with Marriott.