Why is draught (draft) beer known to cause more hangovers than bottled beer?
Any alcoholic drink will cause a hangouver if you drink too much. Bottled beer and draft beer are basically the same product, they should produce the same hangover. But it's easier to drink too much of draft beer as they are typically served in larger volumes.
The exception are darker beverages (like wine and cognac), they produce worse hangovers because part of their alcohol is in worser forms to your body then ethanol. I am not aware of any beer containing it.
Headaches from draft beer could be caused by a sensitivity to tyramine. People with this food and beverage allergy should be aware of the consequences of what happens when consuming foods high in tyramine. HealthLine explains why you may have to say no to draft beer: http://www.healthline.com/health/tyramine-free-diets
Because draft beer is disgusting due to insufficient maintenance/hygiene of the equipment involved and thus bad for your health.
"I clean beer lines and you should probably never drink draft beer"