Proving your version is better can be needed for artists who have gotten too close to their picture and can't see the flaws others do or are afraid of fixing the image because they're worried it'll be worse off. Seeing a better made image can make them reconsider their picture, whereas a badly made or unclear example rarely helps motivate change.
Also writing proper advice takes time regardless of the quality of your examples.

Regarding your dragon thread - because you used a very specific cartoony pose, it's probably much easier to assume you are using it as a placeholder to study something else. It's imperative to state your intentions up front ("I want to make a cartoony pose and so far have been copying off this donald duck pose but could folks give advice on that?" or something)

Thanking system is not a waste of time for a couple simple reasons. Humans thrive off the appreciation of others, that is one of the basic functions that makes us want to group into a society.
1. The recipient can thank the poster for their critique, verifying that they have indeed noticed the post and making the critiquer feel better even if the recipient did not reply.
2. Other people can thank the poster for an especially well made critique.
3. It lessens the amount of inane "good job" and "well done" style posts that have no point.

The starbound forums is a place with a system for liking posts that I've hung out at for a bit. After they detached likes from affecting forum titles, it has settled mainly into a "You did well!" and "I agree with this poster!" message.

I don't think that's so bad.

Grimsane: Yeah I did that at first, but it was too troublesome to fix around unweighting the rigid light gray parts (as they're supposed to be metallic and thus not move at all) so I just went manually weighting the edgeloops.
I had never done manual weighting before so it was a good learning experience.

Those proportions do seem better, I'll play around with the model a bit more.

A turntable to help a friend with Nidorina's ear perspective.

It's a bit goofy with the earholes and otherwise starkly undetailed.

Hur hur, actually the omanyte was a joke request by someone, I decided to try to reinterpret it a bit to retain interest in working on it, rather than drawing what I "know".

(Also Photocopier, that shading on the cup is very nice.)

I think the lack of 3d in the middle one's head is because I had more trouble with the design of it. :O It seems I draw better when the design comes to me quickly rather than having to noodle with it a lot...

Shading is probably also a factor, otherwise the cheek-spurs etc would be lost in the lineart.