First, the term "LCC" generally refers to the airline's cost structure, not the airline's fares. Low fares generally follow from the LCC's cost structure, which is significantly lower per seat-mile.
As far as LCC fares are concerned, most major carriers have matched the LCCs in the markets they serve. In other markets, however, fares remain quite high. Here is an example of AA
's fares on flights from Austin to the Washington DC area:
(served by WN
), departing 1/29, returning 2/2: $589
(not served by WN
), departing 1/29, returning 2/2: $1000
fare could be even more, but I assume that AA
has identified some leakage in this route over to BWI
. Flying AUS
on the same dates is $1534.
So, for all of you in LCC-dominant markets who complain about "false advertising" of LCCs, be thankful -- the LCC in your market has worked to bring fares down overall. WN
never charges more than $600 for a round-trip fare -- try getting that sort of policy on a major carrier.