While it could be said to be within Apple's rights as a company to do this, I find it a severe abuse of consumers' trust.
It's kind of like employees of a bookstore coming into your house, raiding your shelf, and leaving you a store gift card because they no longer have an agreement with the publishing company that printed something. (Also a reference to the previous Kindle comments, but it's all in the same spirit more or less.)
Also, I think the moral issues involved here remind me a bit of the whole argument behind the ethics of net neutrality. Corporations being able to control the free flow of information and ideas in ways the government never could creates nasty, nasty loopholes.
It's nothing like getting censored on a website you paid for, as in the case of a website you are going into their server, somewhat like entering their place of business. They can kick out or censor anyone they like. It's their place you're in.
This is the removal of something you bought and paid for from a device you also paid for and carry around in your pocket, and should have a reasonable expectation of being able to use tomorrow.
Their place now extends into your pocket.
Once upon a time, whenever you bought software, you actually owned a disc and could resell it and everything. Now anymore there's often none, and always some ten page long legalese load of shit for you to agree to but not actually read that says you gave the company however much money but don't actually own a thing, but in fact have only licensed it. It could be taken away at any time for any or no reason. Such as complaints from parents which may or may not exist, or that only represent the views of some reclusive fringe puritanical sect with ten members that believes the color blue is an abomination to god and sex is the tool of the devil or whatever. Or Focus on the Family or some other religious group invested money in a company with ties to the company doing the censoring. Or the stuff being censored contains keywords that the company's marketing research finds has an adverse effect on the public's reactions towards buying more of their stuff. Or it may be considered endorsing views better supported by a competitor. Or so on.
This (the more centralized control scheme of software [including essential operating systems that hardware depends upon to work without jailbreaking or otherwise hacking it] that is licensed and continually modified by frequent updates as opposed to older ways of doing things [yeah I got lazy trying to word that last bit]) gives little or no benefit at all to consumers (aside from things like the wonderful bonus of being force fed advertising from the software's providers or whatnot. I've seen no indication from any of my own experience that support is improved. It's always been there.), but great benefits to the companies.
While this licensing bit may have been the case for a long time, we now have a company actually showing that this is the case by taking things back from the customers. I can't think of any precedents for it off the top of my head. (Can anyone else? Excellent opportunity to speak out here.)
I'd just love to see all the developers whose incomes were negatively impacted by this and all the frustrated customers get together, sue Apple and win. It would make such a lovely official precedent for how companies should not behave.

All this said, I think Apple makes great products. They're good for graphic design stuff, and I use their computers and iPods almost every day. They are, however, being total and complete dickheads. Kind of like when they got all bothered by Palm doing exactly the same thing that made them a viable company to begin with. I've been seriously contemplating buying a new computer, and may end up getting a PC laptop over all this. (feel free also to remind me what rotten things Microsoft has done so I either don't buy a new computer at all, or do and put Linux on it) I don't want to spend money that goes to Apple right now too much more than I want to shop at Wal-Mart. And this is a pretty big deal coming from someone who does graphic design with them.

As an aside, I saw the app in question on the G4 spot, and think that any future versions of an application like that should have the clothes fall off as a flat, animated layer to more closely emulate those strip pens. That'd be way cool. Just while I'm on the subject of this app, you know.