If you have a blank Mac because of a problem or HD upgrade, a network install image being sold outside the Mac App Store makes a lot more sense than Mac App Store distribution. OSes shouldn't be distributed in a store that requires an OS installation to even work.
That is what the USB stick is for! No need to download from anywhere. Don't cherry pick what you want to see and leave out the other options.
That's the point. You say it yourself, your machines still have DVD drives. What's the point of going to the more expensive USB drive option ? Again : CDs were cheaper than floppies to produce and were much quicker to mass produce. Going from optical to Flash memory is the opposite move, it makes the media both more expensive and much more complicated/long to duplicate in mass.
Saying we need DVD Drives just because all the machines out there (still) have DVD drives is a poor argument - following that we still would have floppies. I don't want a DVD drive in my next machine. I would need it only for reinstalling the OS (which on MacOS I actually never had to do, but worst case it might be needed). Actually I won't have a DVD in my next machine since it will be the MBA. The future is here.
And if you see the whole picture (distribution, shipping, storage, ...) I doubt that a read-only chip on a USB stick is much more expensive - and you save on all new machines the cost for the DVD drive and can use the space for better things. If it is so much more expensive, why does the cheapest Apple laptop come with a USB stick instead of DVD? Yes it might be a tiny bit more expensive.
As an Air user with such a thumb drive let me tell you this : their design is pure crap and it is not quite as convenient as a real thumb drive. It also tends to get all scratched up when inserting it and removing it because it lacks the proper guides for the USB port.
How often to you reinstall your OS that you keep inserting and removing it and scratching it all up? It should be a cheap stick (not good for anything else) that just sits 99.99999% of its time in the shelf. It's not that this is meant as a 'free Apple branded USB Stick' that you use all the time.