The Ski Pylon IS meant to pull tubes, skiers, wakeboarder, whatever really. Towing another vessel, that's tricky and talk about that later, but that Ski Pylon is very sturdy and trust it WAY more than the traditional tow hook.
As mentioned, the Ski Pylon is rated up to 500lbs, where as the tow hook is rated for 250lbs (not sure, manual doesn't mention it but it's 250lbs for the tower and generally the same). From a physics stand point, that traditional hook off the transom is just held in place into the 0.25" (Probably thinner) fiberglass by 2 bolts. That does't provide much support. The Ski Pylon is like a 2in diameter thick of solid stainless steel, or whatever metal, situated in a metal base. That thing can handle A LOT of force. But, force isn't so much an issue as the torque applied on the Ski pylon, which is force at some distance, and why @scottburns pictures show it so reinforced. So 500lbs of people on a tube, at 2ft up the pylon, thats ~1000lbft of torque. That's why the taller the pole, the torque increases and could essentially break the transom mount, since you can't really bend 2in thick stainless steel pole.
Overall, Ski Pylon is WAY sturdier and stronger than the traditional tow hook and I've personally towed boats and chose to use the ski pylon over the tow hook. I do that because, back to torque, when I tow boats with it, I don't put the rope at the top, where it should be traditionally. Instead, i keep it near the base to minimize torque effects and, factoring in the weight of the vessel torques are similar.
When it says 500lb weight limit, not the best way to describe the limit, i think. 500lbs, on tube doesn't mean much, like 3 adults doing 5mph is just as safe as doing 50mph? Not even close. You have to factor in speed and lbs is terrible unit of force. I think the limit is calculated doing 25-30mph, can't remember exactly, but 500lbs doing 25mph would give you similar forces if you tow a boat doing 5mph. Load wise, they're about the same. So I can vouch for how strong it is and more than capable of towing tubes.