I think it has mostly to do with scope of awareness for the developer. The IDE provides a macroscopic view of the developer's work context. You can simultaneously see class hierarchies, referenced resources, database schemas, SDK help references, etc. And with so many things affected by, and affecting, your keystrokes, and the expanding volume of architectures and architectural intersections, it gets more and more difficult to work solely from one island of code at a time.
OTOH, "just me and vim and the man pages" gives me a much leaner microscopic - but intense and precise - view of my work. This is ok if I have a well-designed, well-partitioned, sparsely coupled highly cohesive codebase built in one language with one set of static libraries to work from - not your typical situation, especially as dev team sizes grow and reshape the code structure over time, distance, and personal preference.
I'm currently working on projects in Flex and .NET. One of the nicer things about Flex is how few different ways there are to accomplish a standard thing - pull data from a database, open/close/read/write a file, etc. (Yet I'm using the Flex Builder/Eclipse IDE - a typical heavy-weight example like VS, because I'm still learning the basics and I need the training wheels. I expect to evolve back to vim once I'm confident of my patterns.) In this view, I can do what I need to do professionally by knowing a few things really really well.
OTOH, I can't imagine getting to that point with .NET because the view I'm expected to maintain keeps expanding and shifting. There much less conceptual integrity, and over several developers on a project over several months, much less consistency - but the IDE supports that, maybe encourages it. So the developer really needs to (and can more easily) know many more things adequately. Which also has the benefit of helping them answer (or even understand) a lot higher percentage of the questions on StackOverflow. I.e. we can have a deeper knowledge stack. And we can respond to a wider variety of help-wanted ads.
Things can go too far in both directions. Maybe with the "editor-only" scope, it's like "if you only have a hammer, everything looks like a nail". With the IDE approach, for whatever you want to fasten together, you have a broad selection of fasteners and associated ranges of tools to choose from - nals/hammers, screws/screwdrivers, bolts/wrenches, adhesives/glue-guns/clamps, magnets, and on and on - all at your fingertips (with a wizard to help you get started).