Except that some of the investment that Amazon does goes to code that is also useful for the home robot. Amazon can afford it - probably saves money - so they make the investment. then they come along later and realize that the home robot is in some way affordable as so many of the parts needed already exist.

Of course I cannot say when it will affordable. It may be Amazon has to solve the last remaining hard problems and then the R&D is paid for: all that remains is packaging and marketing, it may be thousands of hard problems remain. (I'm guessing someplace in between) I also don't state what the home robot will do. May the home robot just picks up the kids toys when they are done but can't do laundry - even though I want the laundry robot more the toys only one is still useful.