Consumer skis are made with a thicker edge so that they can be tuned more often and are more easily repaired if edges are damaged, given that there's more to grind off. Race stock skis come with thinner edges because, as stated above, P-tex is faster than metal.
Regarding tuning, Ted Ligety stated in an interview with Ski Racing:
I like my edge super thin. When the skiâ€™s thinner itâ€™s easier to roll up on the edge at the top of the turn. With the new skis Iâ€™m having them design itâ€™s thinner the whole way down. Itâ€™s almost like an ice skate. On an ice skate itâ€™s easy to roll your ankle. When you have a bigger platform it takes a lot more leverage to get it rolled back over. Iâ€™m talking about the exact same radius, but a skinnier ski the whole way. Then the sidecut flares out up here at the top a little bit. I want to eliminate that because when youâ€™re crossing the fall line thatâ€™ll hook up and pull the ski across too. If you look at these, the edge is super thin. Just that small amount you can definitely feel itâ€™s easier to come in. When the ski's brand new, itâ€™s really grabby, hard to slide the top cleanly.
That's easy for someone to say when they're not paying for skis...