Yes, that's a bug in the sample.
I strongly suspect it was from a pre-release version where that syntax may have been supported. I expect it's still showing up under "Future Versions" because at the time it was written, it was about a future version.
This syntax certainly isn't supported in C# 4, which is the only future version which has been publicly acknowledged.
It's a bug as Jon mentioned. In addition, the samples incorrectly list nonexistent methods: Fold and EqualAll. They were replaced by Aggregate and SequenceEqual, respectively.
Yes, we just updated most of the 101 Samples with new code that should be less plagued by these kinds of problems. We posted a lot of new code, and there are still some glitches, particularly around spacing, but hopefully we are in better shape than we were. Try accessing the link now, and see if it looks better:
http://msdn.microsoft.com/en-us/vcsharp/aa336758.aspx