Getting cheap tablets into the hands of the poor masses in a similar way to the whole One Laptop Per Child initiative is a noble initiative, but I'm not convinced that we need to be sending computers to children in third world countries, when more basic necessities like clean water, enough food, shelter, electricity, and schools for more people/children in general would possibly be a better expenditure of money.
However, making technology cheaper as a whole is without a doubt important, and is happening everywhere all the time. I agree about the psychology and pricing of tablets. The market needs lots of software/apps for the tablets to make them a justifiable expense if the average consumer and not some tech enthusiast is supposed to purchase a tablet.
With the rise in programs made around smartphones, the market was ripe for the introduction of a tablet now that the software is to a decent level.
The price is also a large factor in adoption, as you pointed out. I've seen a lot of people in here recently with cheap Android tablets from China and Taiwan and other Asian countries. The cheap no-name devices are starting to see adoption by the masses, but unfortunately, the companies selling the cheap tablets are not doing a great job in designing and supporting their products. Because of that, many people have problems with their devices and get discouraged by their purchase.
The devices from the big name companies are still very expensive and still do not always get good support. Only time will tell how successful tablet adoption will be.
The XOOM appears to be coming in a Wi-Fi only version and a 3G/4G/Wi-Fi version. The 3G/4G/Wi-Fi version looks to cost about $800 USD in the US, but I haven't seen any word on how much it will cost in Europe. It will, without a doubt, be very expensive.