It's an interesting website but I would not make assumptions about salary levels too soon.
I doubt the average salary for a practice area is ever the same as for a practice as a whole because you will get different numbers of people at different levels; even if you had complete uniformity in remuneration levels by practice area (which is unlikely in itself if you are including all employees up to the top). There might be exceptions (Accenture's North Korean office?, some start-up consultancy practices?). A better comparison might be by consultant grade but you are unlikely to get a McKinsey consultant to release this/these on the forum, especially if they work in the technology office! Good luck. P.S. Have you looked for any industry figures, some surveys give you averages for technology sector consultants?