One problem is that people think about seniority as expert level in something.
In my terminology, when you are a senior you need to be a near expert in whatever you call yourself a senior within.
If that's .NET/C# like the author refers to, you must know how all (the esoteric) features of the language (e.g C#) behaves, you must know IL, WinDBG for advanced debugging and the things along those lines.
So many developers claim something that they are absolutely not, which is experts or senior in a technology.
It's IMO much harder to become an expert in something than to learn a subset of a set of technologies. Much harder actually.