Dan: A lot of musicians have some of the gear they NEED but not much in terms of stuff they could REALLY use.  This may not apply to all musicians, but for guitar and bass guitar players they have the instrument but not a good enough amplifier.  Since they can be quite costly if you do not shop around smartly to find great values, it takes time and effort to find a good one.

There are also many different brands and qualities.  If you are looking for a perfect gift and the comfort of knowing that you got the RIGHT thing, go with Fender amplifiers.  For both the electric guitar, acoustic electric, or the bass electric guitar, Fender distributes the highest quality and most durable amplifiers.  So even if someone you know has a guitar, do they have the right amp?

Grace: This is a great gift idea!  You are right that so many musicians have a suitable instrument but not the right system to make it come out sounding its best.  People who play acoustic guitars that are not amplified do not have to worry about this problem, but if you do need amplification, it is a problem.  $2000 Gibsons sound terrible on a $60 25 watt amp.