This seems like something that the Harvard Business Review should have written up many times.
Still ...
Successfully being senior is not the same thing as staying current and keeping up with
technology. This is
PART of the job, but the junior folks will be doing this,
too, and they are less expensive and often more enthusiastic. A sergeant in the US Army
isn't expected to be a better private than the new recruits. The sergeant has
extra responsibilities on top of that of the privates.
Likewise, a senior technical contributor isn't being senior if he or she is simply better
at the current technologies than the recent hires. Being senior involves more than that.
In general, as you become more senior, but still technical, the job becomes less just about
just implementing solutions (though I believe that skilled senior technical folks should continue
to do this). Instead,
the job becomes more about deciding or helping to decide what should be
implemented and providing technical help, leadership and guidance to the more junior members of
the team doing the bulk of this implementation.