....Coz it's not unusual to say, "I like the gift you gave me so much, thank you!" so it'd not be unusual to say, "I like the post you just made, thank you for taking the time to write it/for saving me the trouble of having to write it/for wording that better than I could/for the good laugh that made my day, etc.
I think it goes back to the 1371391073237 reasons people might've thanked a post when that is all we had: sometimes there was just one reason (you liked what was said so said thanks); sometimes there were more than one reason (you agreed with the post, you found it funny/enlightening, etc...in which case thanks was the ideal response). Now that we have both responses, you can cover all bases more appropriately if you like it and are grateful for whatever you gained from it....