Currently all implementations suck if you don’t have one of the few supported HP printers†. Maybe a more encompassing solution would have helped the TouchPad (for example the ability to use any printer in the network) but I doubt that for such a feature alone TouchPads would have sold that much better.
Apple already had a feature implemented (in one of their betas) that allowed you to use printers connected to your Macs but they ditched it for some reason. Maybe technical reasons? Maybe politics? (Could they have a deal with HP?)
Having one (or even a few) HP printers that support the TouchPad – as you suggested – is demonstrably not good enough. The TouchPad flopped regardless.
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† Android is a different story but as far as I can see not a very pleasant one.
http://www.apple.com/ipad/features/airprint.html
All of the printers that support AirPrint are made by HP. AirPrint is really just an adapter on top of HP's proprietary ePrint. I believe ePrint even lets you send documents to the printer over email from a computer or any other device.
http://h71028.www7.hp.com/enterprise/us/en/ipg/HPeprint-solu...
Google Android also has an adapter to directly print to HP's ePrint printers through Google's Cloud Print
http://www.hp.com/united-states/campaigns/hp-eprint-google-c...
Normally Cloud Print for Android (or any other device) works by running a print server which is bundled with the Chrome web browser on a Windows PC connected to a normal printer. Instead with ePrint the network print server exists on the printer itself so you can send documents to it directly.
Obviously, the HP TouchPad works with ePrint natively out of the box. So all of these mobile operating systems are designed to work with the same line of printers which are all made by HP.
Technically, Android can work with more printers assuming you want to rely on a Windows box to act as your print server.