PC's are more manipulative. They give you more options on what you can do with the things you have. For instance, I am a programmer. I can't write programs with my tablet, but I can write programs with my PC. They are the basis of all computers. I like the hardware better as well.
For those looking to replace a traditional desktop PC and are willing to spend only a low amount, other computing options may be a better value for them. Today's smart phone and tablet offerings provide sufficient computing power and form factors to replace the desktop PCs of old. In the sub $100 PC market, smart phones and tablets can do most of the same basic functions.
Personally, I would much rather save up money for a nice touch screen tablet, than quick blow it on a PC. However, if you don't have a lot of money at the time, a PC may be your best option, especially considering the extremely high prices on smart phones and tablets.
A $99 PC is not sufficiently costly to accomplish the barest necessities and will deliver nothing but frustration and fail at the very tasks it was intended to complete.
Meanwhile a $99 smartphone or tablet may well be subsidised from the network provider, in the hope of selling data services or app-store owner in the hope of cashing in from continued use (eg. Kindle). This incentivises the creator to create a good strong user experience, increasing the likelihood of continued use and thus opportunity to profit.
No, I do not think that a $99 PC is a better purchase then a smart phone or tablet because if a PC is GOOD and made of good reliable parts then the price would be greater then $99. A smart phone or tablet is worth less because they are usually inable to do less then a PC.
There is a large market for affordable smart phones and tablets. You can easily get a quality, functional smart phone or tablet around the $99 price point, particularly if you are signing up for a new plan with your cell phone provider. These devices are designed to perform the types of tasks most people perform on a daily basis. If you are looking for something to check your email on, then a $99 PC might be worthwhile. But why not get the added benefit of portability, as well?