[acdha]

Google refused to allow you to pay for them? Each of those services could trivally have had some combination of ads and paid services but Google's management made strategic decisions to put resources elsewhere.

Only using paid services up front might seem to help but one look at the way Google Apps has been in maintenance mode for years suggests that even that offers only limited protection.

[wstrange]

Realistically, how many people would have paid for something like Google Reader after getting it for free for so many years? I think it would be a tough sell and you would have witnessed a lot of complaining...

On the other hand, the negative PR they have gotten from Reader (it's pretty much the poster child for the "Google cancels products" meme) - they probably should have kept it around, even if it was not strategic.

[acdha]

I'm pretty sure anyone working at Google knows how to put ads on a free service but in any case, I saw a lot of people calling for a paid option in the period between the de-featuring for the botched Google+ roll-out and actually closing the service down. That would have been a natural approach: free version has ads with some sort of “Pro” option to remove them.