People grumble because they have experienced change, and the change was for the worse. In my recent experience PayPal, Gmail and eBay have all changed, and not for the better. The new Rails and Bachmann sites have also had a lot of criticism in these pages. If the site is/was poor, by all means improve it. People get apprehensive when they can't see anything wrong with what they've already got, and cannot readily see room for improvement, only the scope for making things worse unintentionally.