I don't agree that it's the UI that makes the difference here. I think it's the context. In an "email" like context, it's not uncommon to write a few sentences.

I don't agree that it's the UI that makes the difference here. I think it's the context. In an "email" like context, it's not uncommon to write a few sentences. However in a chat its usual only to write one or two sentences, wait for a response, and then respond to that again. Its not an mail that your sending and hoping to receive a response later, its instant chat. If you had just said "Hey, what a show last night! Pretty sure my ears will be ringing for the next week. lol", and then waited for a response before writing anything more, then you probably wouldn't look that desperate. It's not about the UI, it's about the expectations for the medium.