This may be true for TED (never been) but for most tech conferences I've spoken at the presenters are still putting together slides for their presentation right

This may be true for TED (never been) but for most tech conferences I've spoken at the presenters are still putting together slides for their presentation right up until they talk. This tends to get the latest stuff in. Not to say I'm disagreeing with you -- quite the opposite, in fact. With rare exception, during most of the conferences I've been to the "hallway track" has been more valuable/informative.