I think the current top-heaviness of the payouts is for marketing reasons, and I think as a marketing strategy, it's probably a good idea. The IPT has now claimed "the biggest pay-day in the history of professional pool" in every one of its events, unless I'm mistaken. They paid out $150,000 to Sigel (which may not or may not have been the biggest ever, not sure on that one), then $250,000 to Efren, $350,000 to Thorsten, and $500,000 to the winner of this event. If they manage to get these all on TV eventually, it should be a good way to grab people's attention.
In the interests of making the tour more fair in the future, though, the pay-outs should become somewhat more evenly distributed, so that the players that consistently make the top 5 or 10 will win at least as much as a player who won a single tournament but didn't do well in any of the others.
-Andrew