Trust, that's why people buy

More people are buying air travel on the Internet than ever before.  Southwest Airlines leads them all with the highest percentage of customers booking on their web site.  The reasons for this are that their route structure is fairly simple (as is their web site) and the pricing is trustworthy.

I believe that the primary reason for not buying via a web site is lack of trust.  Whether it's the airlines' web sites, Travelocity, Expedia, Orbitz, ITASoftware or others, if you aren't sure that you have the best price, you'll keep looking.  In my opinion, ITASoftware has the most useful interface, most flexible display options and highest confidence factor when it comes to the prices they show.  That said, none of the web sites show complete prices (that's why a travel agent can be very beneficial) including all consolidator/wholesale prices.

I believe that Northwest is the worst offender when it comes to pricing and lack of trust.  You've seen my comments about the fact that you only see their special prices if you enter the secret code on their web site and you only get the code if you enter via their 'view all promotions' part of their web site.  On top of that, I have various coupons (from canceled/delayed flights) with other codes some of which are redeemable on-line and some only via phone.  If their objective is to lower their labor costs by keeping you off their '800' number reservation center, they are failing miserably.

Until you can trust the site, you're not going to buy.  Most of the major airlines have some routings which are simple enough that Southwest could be emulated.  They would be wise to try where they can.