Catching the Plane?

Why do so many Romantic Comedies end with a race to catch a plane? It makes no sense to me! It's like if the person doesn't catch that plane, then the person's fate is sealed and they will spend the rest of their life alone. Just got done watching "Life As We Know It" last night, and I can see why she rushed to catch him considering he's flying to such an obscure place like Phoenix. I love how she buys 3 plane tickets to get her to the gate to catch him, yet apparently she can't buy a plane ticket on the next flight to Phoenix. Of course that's the last plane that will ever fly into Phoenix ever again. Are all these love interests flying to Brigadoons or something, where the town will disappear at like midnight and not appear again for 100 years? That's the only reason I can see for a person to believably have to catch a plane or spend the rest of their life alone.