Marc Jutras said:
...I usually either don't have the time to write something or I just don't know what to write and a simple "I like it" doesn't seem relevant. I look at the galleries mostly from work and have only a few minutes to do it. Also, I don't analyse pictures much (as well as any other art form). I go wih my gutts and it's more a "it works for me" or "it doesn't work for me" thing (professional habit of sorting hundreds of pics daily and deciding within a second, I guess). I also usually feel like I'd be stating the obvious which is something I don't enjoy much.
Very personal 0.02$...
Hi Marc -- That's all reasonable.

I have heard elsewhere criticisms of people leaving encouraging but non-specific comments such as "Good shot!", but from the recipient's point of view it's friendly and encouraging. Any kind of positive comment is pleasing and may inspire future effort. I think of this as part of the friendly mutual support that is so nice in the RFF community.
So your comment may be simply a friendly helpful gesture... and it's human nature that receiving this encouragement makes it more likely he'll comment on your shots too.
And getting into more detailed and specific comments, even criticism in a helpful supportive way... Yes, it requires thought, analysis, and in this way it's as useful for you as for the photographer. When you make the effort to examine the photo, think about it, relate it perhaps to other photos of a similar or contrasting nature, struggle to put your thoughts into words, etc... This is helping you in your photography as well in developing these analytical skills.
I don't know whether it's good to respond to comments about my posted photos, as my responses could pad the comment count. So I try to make any response more than just "thanks!" But I'm always grateful for any comments, as plus or minus it's better than total silence!
To the degree a numerical rating would make thoughtful comments less likely, it's not a good thing. I'm recalling the frequent posts in Photo.net complaining about low ratings on their picture(s) and asking why... and this so often turning sour.