Here are a few reasons:

• You still have no way of installing non-app-store apps, even 4 years later.
• Only now have we been able to get the mobile data on more than one cell phone provider, which is a default feature in other countries.
• Apple has been booting GPL apps (or the developers have been removing themselves) from the app store.
• The Maker Bill of Rights: If you can't open it, you don't own it
• I can't put my iTunes / iBooks content on other devices, unless they came from Apple, running Apple software.
• The iPad is designed to be used by exactly one person. Do they expect every member of a family or each employee to have his or her own?
• ...and many many more. Including one new wrinkle:

Apple responds: we want a cut of Amazon, Sony e-book sales by Jacqui Cheng:

Apple doesn't allow apps to sell content to users unless that content passes through the official Apple ecosystem, where Apple gets a 30 percent cut.

If an app lets users access content that they purchased via Amazon's website, for example, then that same app must also let users buy the same book via Apple's own in-app purchase system. If the app developer doesn't want to use Apple's in-app purchases to sell content, then the app can't access content purchased elsewhere either.

On the one hand, making things easier for users, I can see how you would arrive at this decision. On the other hand, taking a binary approach to it - you're either in or out - is what really boils my beans.

Is there anything better out there? I really haven't tried non-Apple tablets, but this is one very good reason.

When recommending a touch screen solution to a local arts organization, I urged them to get a touch screen PC and develop a website that is optimized for touch instead of getting an iPad,. It ended up being cheaper and easier to develop, including easier for them to lock down, so patrons couldn't use the other apps in their lobby. Also, if they decide they would rather use different software, say Ubuntu instead of Windows, they have that choice, and they should still be able to get support from the hardware vendor.

Are they missing a lot of other iPad stuff? Yes. However, this machine was intended for a single purpose. The iPad is not a one-trick pony, and it comes with a lot of baggage. See above.