There are two reason to use XML comments opposed to plain English:
If the comments follow the correct format they will show up in IntelliSense, meaning when I use your class I can see that
int a
is supposed to be the count or whatever the same way I see helpful info when I'm using .NET methods,If you use the XML formats Microsoft supports you can create html (or other formats of) documentation using SandCastle or similar third party utilities.
So, if you're taking the time to write comments, you may as well make them the XML ones that VS encourages.