There's also an email etiquette in the corporate world to not blow up people's email inboxes with unnecessary replies (i.e, "thank you," "gotcha," "
," etc. When I worked in that environment, the "thank yous" alone could number in the hundreds on a daily basis, especially when sending out group emails, so unless there was something substantive to reply with, we all just skipped it.
Speaking of group emails, when you hit "reply all" simply to say "thank you" to the OP, and especially when many recipients respond, all those other people receive the "thank you" as well - totally frustrating.
That being said, I think that in this forum, and in social settings, a "thank you" response is appropriate.