In general getting upgrades is not like cash. With cash they will oversell one class of rooms (like standard view) knowing they can always upgrade someone (making a little magic for them.) Like a few years ago the Value resorts where WAY over sold, so a bunch of people paying $79/night where moved to SSR.
However, since this is a timeshare. They can only rent what they have, when the last Standard view room at BLT is gone, they can't book any more Standard View stays at BLT. Forcing the next person that wants to stay at BLT to take a Lake or Magic Kingdom view.
Now that said it can and does happen. Because there are limited number rooms held in reserve for emergencies. Like a broken shower, or a leaky window or something like that.
In those cases the point difference comes out of a reserve account that DVD (the developer) holds. So no you don't get charged with the difference. However, don't plan on it. Remember the rules for timeshares are different than those for hotels. With a cash reservation, the hotel operator is just out the difference in cash. With
DVC, the point pool is fixed (when the resort is built), and if "upgrades" where given away the pool would become unbalanced.
Note: this is also why you can only bank/borrow 1 year. It helps keep the pool at the right level. Sorta a conservation of points.
johno