Besides, if everyone switches the kettle on during the commercial break, you just shift the spike forward a bit.
And yes, tea is that popular. In my office, each person will typically drink 3-4 mugs of tea during the day. Many people continue with at least two mugs when they get home.
Many people will have a morning coffee, but tea is drunk continuously throughout the day.
Oh yes. People drink tea throughout the day. Basically black tea with milk and depending on the person sugar. Water is boiled in an electric kettle and poured onto tea bags.
Is there some etiquette that says you must wait until the T.V. show is finished before you may start making tea
It's not an etiquette thing, but more just co-incidence. When a TV show is over, lots of people might want a cup of tea and so it's more that lots of people are doing the same thing at the same time (i.e. a spike).
(why not switch the kettle on during a commercial break)
Channel that have ad breaks would have them every 15 → 20 mins, so the water would go cold.