Hi Astronaut,
I think it's very unfair to say that encouraging donations is all about making tons of money (which, as you say, is very unlikely to happen!). And comments and ratings are just as valuable too.
If you're an indie developer in my situation, say (e.g. a full-time job and very little financial resources), then small things can make a big difference- whether it's financial (e.g. is it worth spending £90 to buy an audio recorder to improve sound effect quality in a game?), psychological (motivation can be very important- if people don't get any encouragement, they might just decide to spend their evenings sat on the sofa watching telly instead), feedback to improve the next game etc. etc.
All these things are vital, and the people who play the game are often the deciding factor on the outcome. All too few people actually do provide feedback and this is a huge problem.
Sure it might be a very minor annoyance to get one notification after every download, but you've got to weigh that up against, for instance, a dev who's spent maybe a year of hard work in order to get a game finished, which is being put out for free.