Southwest and Easyjet have made a huge success of sticking to the LCC model..
True, however the circumstances were a bit different. The 100lbs gorilla in the local market with deep pockets started a competitor to wedge them in the low cost space.
Not sure of the history of Easy, however SW grew very slowly and evolved
into it's market niche (see
NUTS!). Every new city pair it started had to be profitable
from the first flight. If they couldn't make it work, they waited and figured out a way to make it profitable or never entered the market.
This isn't the history of Virgin, or Jetstar for that matter.
edit: One the the NUTS! book
reviews mentions another interesting book on the formation of SW:
Southwest Passage: The Inside Story of Southwest Airlines' Formative Years