I'm not a singer but if people are starting to give you constructive criticism, it's maybe because they now care enough to do so.

When someone is starting out, most people are tactful enough not to make adverse comments and some even try to "be nice". Mind you, if you've been singing for about ten years, it seems odd that people are just starting to comment now.

However, on the whole, I'd take it is a sign that your singing is actually improving(Unless they specifically say otherwise)and it's more likely that they wish to see you progress rather than "sour grapes". If it was the latter, it's unlikely they'd tell you to your face.