Why does tequila seem to have a greater propensity to cause a headache than other alcohols?

Possibility. In addition to amount consumed, darker liquors like red wine, brandy, whiskey, and tequila may contain chemicals called congeners -- kind of like impurities -- that contribute to headaches. If you're sensitive to these, they might give you more trouble. http://www.hopkinsmedicine.org/neurology_neurosurgery/specialty_areas/headache/conditions/hangover_headache.html.
No relation. All alcohols can cause symptoms such as headache but it depends on your metabolism and the amount ingested. Remember that one "serving" is only 1.5 oz. I'll attach a photo to help explain. In addition, see "alcohol 101": http://www.Wwu.Edu/chw/preventionandwellness/aodwebpdfs/whatisonedrink.Pdf.
Individual. The rate at which you consume the alcohol, your relative state of hydration, blood sugar, kidney & stomach health, and general health contribute to hangover headache. Tequila is concentrated with minimal taste, so it's easier to consume too quickly and lead to rapidly rising alcohol levels, low blood sugar & dehydration. See http://www.Mayoclinic.Com/health/hangovers/ds0064/dsection=causes.