The "PC market" refers to current sales. "Installed base" is the term for the metric that includes the languishing WinXP machines.
Ah yeah you're right. The 1% came from some guy extrapolating Samsung's sales of Chromebooks to mean the whole Chromebook market...
Chromebook sales are a much bigger part of current PC sales. And vendors do keep expanding their Chromebook lines. If it was a failure they wouldn't.