RMS is legendary for not getting up before the crack of noon. "Breakfast" is for "mornings". he has neither.
Also the type of food. If you sleep in on a Saturday until noon, you'll probably tend to want breakfast food when you first wake up.
The time of day is far behind those two factors for what constitutes breakfast in popular usage.
It's 9am on a Saturday here and I just ate two slices of cold pizza. Not everyone desires "breakfast food" first thing in the moring. :)
Even Wikipedia doesn't have a strict definition. I propose a standards committee meet to disambiguate this once and for all.