This discussion has nothing to do with the future of the internet (no, it's not going to go away, though more and more services will move to direct traffic as described), nothing directly to do with "design principles," nothing to do with a guiding philosophy, nothing to do with "viewing your pictures in the cloud." We just want to be able to delete a single photo from photostream without having to turn off photostream on all devices, sign in to iCloud, and then delete everything there, and then turn everything back on. Seriously -- common sense, people?
Yes, at present, the workaround is to keep photos from being added automatically to your photostream.
Photostream and iCloud in general needs to be able to mirror any laptop environment in the way files are found and organized and then reproduce it on the iPad and iPhone, even if it's only accessible via individual app. Apple is consistently behind in providing this capability, but does provide it eventually with future updates: think about folders for apps, the way photos can be organized in iPhoto by faces, events, etc. An extension of this design lag would be in the way text documents are organized in Work on iCloud. We should be able to group documents somehow -- if not in standard folders, then classified by "projects" or something like that. What they have now is awkward and inefficient.
I would suggest that these current limitations actually seem to violate Apple's design principles and philosophy, which seems to be focused on simplicity, flexibility, elegance, and being user-friendly via intuitive interfaces. These principles are the reason I like Apple products. I like Apple products for the same reasons I like certain kinds of cars, watches, shoes, and pens. But you need to understand that of the four, only elegance is handed down by designers. The other three are determined by users. As a result, it's rather counterproductive to tell users that they're wrong, when the design is supposed to be carried out with them in mind.