Sure, Temis, but you rent all kinds of films and regularly keep your queue stocked. You are a much different rental user than, say, someone of my parents' generation. And I think there definitely will be a backlash from those kinds of customers.
The average person doesn't have the slightest clue when DVD/BD release dates are unless they see it on TV, in which case it's in their memory for oh, another 2 minutes tops unless it's a movie/show they're interested in.
I'd be willing to bet a large sum of money that if you that if you asked 100 random people about the DVD release date for a popular recent movie, 90 of them or more would not know the answer. This 28 day delay simply isn't going to matter for the vast majority of people.
Here's how it works. You see a title for sale in the store, and think to yourself, I want to rent that. Then you try and rent it and Netflix says it is not available. Repeat experience often enough and you're going to lose customers. Of course, it's only one studio, and the instant streaming library is a nice off-set.