The x => Factor

I may be swimming against the tide here, but I don't understand why it has become an idiom of C# to use x as the parameter name in lambda expressions, as in:

var matching = list.ForEach(x => x.Version > 1)

You wouldn't expect to see

foreach(var x in list)
{
 if(x.Version > 1)
 {
    yield return x;
 }
}

I suspect it has a lot to with conciseness. Whilst I highly value conciseness, I value readability over conciseness.