I do agree that King does not place much importance on Watson's character (her portrayal of him reminds me more of good 'ol loyal, simple Samwise Gamgee). But did I interpret Holmes as cruel in that scene? No, not at all. When I read it, I really felt that Holmes was just so... tired. Tired of everything. I really could sympathize with that feeling of just being so drained - emotionally, physically, and mentally - that he just wanted to escape. He needed more than a "nice holiday", he needed to literally disappear for awhile and get his head/heart/soul back in order. It didn't seem cold to me at all.

Those are my thoughts, anyway.