Many in the biz would say that anything less than 50% profit for a small software-driven startup is on the knife edge of disaster. Also, the economics of software/services are different than physical products: once you reach breakeven, every single incremental sale is almost all profit except for the cost of advertising, etc to acquire the customer. I'll take 100 customers @$70 profit over 50 @$100 any day.
Cost of customer acquisition is key in any business. Realize that the Apple Store is a form of advertising, payable only for actual sales (i.e. CPA advertising). If you've ever done any Google, etc. advertising, you'll know that 30% advertising cost to acquire an actual customer is pretty darned good!
If you're going to anonymously call the cops on your loud neighbors, don't try to talk to the neighbors first. They'll know it was you and not one of the other neighbors. Basecamp have cut off any possibility of a clever separate product by shooting off their mouths. Apple will now be watching them extra-carefully and will warily look at any "premium" offering with the presumption that it's a ruse to dodge their TOS.
In any event, $99 is a major price point. Psychologically even just $100 will encounter significantly higher price resistance, let alone $140. You can't dodge that. ("Price point" is a different concept than "price," marketing vs. economics. $99 and $100 are the same price, but very different price points. Silly, but that's people for ya.)
Parenthetically, some other commenters seem to feel that charging a % of the sale is somehow problematic, yet that's effectively the way that advertising prices work out IRL. Advertisers with higher-priced offerings can naturally afford to pay more $ to acquire customers and bid up ad prices in their niche accordingly. It's amazing how much a single Google AdWords click costs for life insurance. Or major military hardware.