So that's intentional...just because we don't have much real estate on mobile. So we choose to show the person who created the thread, rather than last update.
@JeffreyWay for me, it's confusing. Replies counter increases while username remains, looks like a bug, especially when I got used to other behaviour on PC.
Update: also it makes difficult to search for last reply in long threads. You don't know which username to search.
@Glukinho Okay, I'll have a think over the weekend. We do show the last replier if the browser is slightly wider (around tablet size). But you're right that mobile doesn't. Will see what we can do!
@ghabe Eh, I think it's not worth the effort. We'll announce big updates to the site, but page refreshes wouldn't qualify. You can see for yourself what has changed next week.