Notice the sensation first, not the flavor

Question:  Boiling water...why is it used for brewing oolongs? 

Answer: Because the "Experts" do it.

Yes they do (at least the honest ones), but here's why.  The teahouse owners buy from producers or distributors that use boiling water, whether in a bowl, gaiwan, glass, or competition "mug".  Not knowing why, some retailers use the same method.

Oolong is brewed for longer periods of time in boiling water to allow people to test for bitterness and astringency, which show up more clearly with high temperature water.  Tea is brewed longer so that the underlying characteristics of the tea cannot hide.  Unacceptable bitter or astringent levels are revealed in a tea with a poor base.  However, though manipulation of heat, oxidation, roasting, brewing and chemicals, a poor tea base can hide behind decent aroma and flavors.  Inferior tea at superior tea's prices - it's way too common.

If I were to buy tea from someone I didn't know, I'd watch to see how they brew my tea.  If they cheat, then I'll ask to brew the tea myself.  I generally brew any tea that is bought in a gaiwan myself to test what it will taste like in a regular brewing environment.  That's usually when I taste to see if the aroma, mouth-feel and flavor will be acceptable. 

Good tea can withstand boiling temperature, but it may not be at its best.  Sub-boiling tea makes Taiwan oolongs open up wonderfully, and as a secondary benefit, will result in more brews for the tea.