Peg Plikos are rated to 88 lbs. The seat is rated to 45, but there is an assumption that an older child might ride standing on the mini-step on the back. I don't find that really works well in practice (you need a buggy board to make it comfortable), but the stroller is made to hold the weight. It's a good WDW stroller because it folds VERY compactly, but it is still rather heavy, at 18 lbs. My 43-lb, 47.5 inch 5 yo still fits very nicely in the Pliko, and it is still easy to steer. (It is not the seat that goes if you put too much weight on a stroller; it is the wheels. The axles start to bow, and the wheels won't turn easily.)
Like all Americans, babies are getting heavier, too. When my son was born in 1997, most infant car seats were only rated to a maximum of 22 lbs. Most toddler carseats were only rated to a maximum of 30 lbs. rear-facing at that time. Now, most toddler carseats are rated to at least 35 lbs. rear-facing, and some of them go up to 40 lbs. Since you can turn a child front-facing once he makes 20 lbs. & 1 yr. old, that means they are mfr'ing these things for 35 lb one year olds!
Of all the gear purchases you make for a baby, the stroller is the one most deserving of serious investment, because it is the one that stays in use for the longest period of time. Most people use them several times a week until a child is around 2.5, then sporadically for another year or so, and once-in-a-while for major
walking outings (like WDW) up to about age 5.