There is a saying along the lines: Anyone can build a bridge that stands up. It takes an Engineer to build a bridge that just barely stands up.
That may be trite, but there is a point, quality engineer is often more about leaving things out, rather than just throwing in everything and the kitchen Sink.
Tablet PC have been built for several years with the "everything and the kitchen sink" marketing check-box design ethos and they have been failures. They usually end up as slow/heavy/expensive mediocre laptops with mediocre tacked on touch capability.
Apple instead is "thinking different", they actually made tough choices to deliver a Fast/light/inexpensive touch device. Making choices though always leave the door open for more complaints when someones pet marketing check-box isn't met, but in the end it may represent more solid design, delivering a better user experience (hard to quantify).
Perfect? Heck no, I would like an SD slot for one thing, but I realize that if you meet everyone's check-box list, you end up with a compromised Frankenstein device.
This is a very important point.
Apple's ability to bring many of these devices to market successfully has as much to do with what they left out as what they put in them.
Every marketer wants a big spec sheet with a bunch of check boxes to fill in, but that does not actually make a cohesive machine. Being greater then the sum of your parts is something to be proud of, and Apple has accomplished a couple of times now.
There is no doubt in my mind most of the things people think Apple should have done with the iPad they actually did try and test in some form and ended up rejecting, either for the short term or forever. You shouldn't add features and items to something just because you can kludge them in there, when if you wait and take your time to do it right, you will be much better off.
I have no doubt that more will get added to the iPad over time, as Apple changes their minds on somethings, finds different ways to implement other things, and cracks the right way to accomplish even other things. In the mean time they will still make a very solid and highly usable device, which at the end of the day is the most important.
Do I want an object I use for 3 month full of specs and then stuffed in my drawer, or do I want something like the original iPhone that still is an awesome tool today. It doesn't have all the features of the later version, but on its own it is still pretty remarkable.
This is what drives me crazy about things like multi-tasking. People act like apple couldn't add multitasking even if they wanted to.. which is not the case. I am sure they have done extensive testing on various methods of multi-tasking on iphones and iPads and will continue to do so. Clearly they have a high standard for what they want it to be though, and for what they want the user experience to be, and they are not willing to compromise that. I commend them for that belief because few companies have cajones these days to stand up to the marketplace and resist consumer pressure and not just rush features to market and not wait to do them right.