> since an IDE that needs extra investments into ReSharper is not that good in my opinion
A lot of people choose ReSharper for "nice" things that often times aren't buying them a whole lot in terms of productivity (e.g. "turn this foreach() loop into a Select() statement" really doesn't buy one much). I'd hardly say that one needs ReSharper to get the full Visual Studio experience.
With the latest versions of Visual Studio (>= 2012), I agree with you, but 2010 and prior still didn't have a lot of the Go To Symbol fuzzy search features that VS now has out of box.
Regarding the LINQ refactors you mentioned, I'd say those are less about gaining productivity than it is to educate the developer in how code can be refactored. A lot of times, those LINQ refactors turn out considerably less readable, but it's a moment to learn other ways of solving problems.
A lot of people choose ReSharper for "nice" things that often times aren't buying them a whole lot in terms of productivity (e.g. "turn this foreach() loop into a Select() statement" really doesn't buy one much). I'd hardly say that one needs ReSharper to get the full Visual Studio experience.