The addition reaction between alkene and gaseous hydrogen bromide: why is it an addition reaction, rather than electrophilic addition?

I have come unstuck on why - despite the fact that hydrogen bromide is a polar molecule - why it does not react with ethene via electrophilic addition in its gaseous state? For example, bromine reacts with ethene by becoming an induced dipole and then reacting via electrophilic addition. Why does H-Br(g) not? Is is to do with boiling temperature?

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• Did you actually read the textbook?? I quote ethene reacts readily at room temperature with a solution of hydrogen bromide in a polar solvent. It is another example of electrophilic addition. – bon Nov 29 '15 at 14:04
• Sorry, I meant to ask specifically why gaseous HBr doesn't react via electrophilic addition. See paragraph down from the one you quoted from. Many thanks, – Ted Rory Nov 30 '15 at 23:41
• Presumably because HBr won't readily dissociate in the gas phase and so there are no ions to do the electrophilic addition. – bon Jan 22 '16 at 10:03