tennis players do have longer stroke arms than the contralateral arm. This does not seem to be due to a selection bias as the mean contralateral arm of the tennis player is the same as the control arm for non-players. Thus there does not seem to be a selection bias for arm length as there does for say basketball and height.
The changes in the tennis player seem to be throughout the entire bone rather than just the ends of the bones. If the changes were due to the growth plate you'd expect the changes to be constrained to near to the ends of the bones but since the changes are throughout the entire bone it's more consistent with plastic deformation.
Baseball pitcher's pitching arm tends to be longer than their non-pitching arms. Many have speculated that this may be due to the stress that pitching arm undergoes. However, many have retorted that people with one arm longer than the other may just be better pitchers. That problem does not exist with instrument players. Longer fingers do not make people better guitar or violin players.
http://www.sciencebuddies.org/science-fair-projects/project_ideas/Music_p014.crapml#summaryhttp://www.heightquest.com/2010/04/bone-lengthening-in-response-to-stress.html?m=1
