Hyperbolic much? I mean, seriously, I get that rules are rules (and am, personally, a strict rule follower) ... And if you want to slam the poster for rule-breaking, have at it. But "endangering lives?"
So, the exact same weight and height child one week is "safe" but the next, post-birthday, is a "danger"? Might be a rule, but doesn't ring true, does it?
I get that they have to have a cut off somewhere, etc. Logically, though, getting an infant, who can't walk on their own, out of a hotel, is going to take longer in a life or death situation (going to get the baby, carrying them through smoke-filled hallways), than a mobile child, so how is one safe and the other a dangerous hazard?
To stay on topic ... Our first trip with our smaller-than-average son (I can usually guess another child's age by assuming that if they're the same height/weight as mine, they are at least a year younger) was when he was 3. Never even occurred to me to make him "2" on the reservation to save money.
Like I said, I'm a rule follower and this never even occurred to me, so no decision required, but while I could totally argue that Disney's prices are absolutely outrageous, I don't think teaching your kids to lie for personal gain is the sort of precedent you'd want to set to save a buck. If for no other reason than it will most certainly bite you in the butt as they age and pull the same stuff you taught them back on you.