It depends on how iconic that character is, and how much that character matters to different people. You, for example, don't care about Ironside as Sam Fisher, but someone else might care about it and not care about Garret.
As for my own personal example: I didn't care too much when they changed Lara's voice in Tomb Raider: Legend, but I did care when IOI said that Hitman Absolution won't have David Bateson as 47's VA (which, fortunately, changed a few months before release).
Because all VA's of iconic characters matter to certain groups of people - they all matter. Unless the VA is dead, unwilling (and can't be reasoned with), or unable to do it (and won't in the forseeable future), of course.
As for my own personal example: I didn't care too much when they changed Lara's voice in Tomb Raider: Legend, but I did care when IOI said that Hitman Absolution won't have David Bateson as 47's VA (which, fortunately, changed a few months before release).
Because all VA's of iconic characters matter to certain groups of people - they all matter. Unless the VA is dead, unwilling (and can't be reasoned with), or unable to do it (and won't in the forseeable future), of course.