There are tradeoffs in every product. Price, feature set, target market, goal. In fact, there are tradeoffs in everything in life. Sony's design choice of a custom OS made some features easy, and other things much harder/impractical.
You are correct, that every buyer, deciding how to use their hard earned money, has a right to expect that the product they decide to purchase will meet ALL their expectations. And if a product is missing essential features that are at the top of a buyers list, then of course that product should be removed from the list of possible products to purchase. Nobody can, or should, dictate what a person should buy. Each person decides what is most important for them, and thus can make the correct decision on what to buy, and what not to buy.
For people who use/need streaming, the WM1x will not meet their needs. People who want a DAP that is very good as a standalone player, and that is what they will value, and use most/all of the time, the WM1x is a good player. For both, there are also other choices on the market, so choose what you will be happy with. It is not that often that we have full control in our choice, so definitely choose what you are happy with.
If the design choices that Sony made in the WM1x do not meet your requirements, then, as in the phrase from Star Wars, "this droid is not the one you are looking for"