I also noticed this same pattern. Until roughly 2008 - 2010 or so, interviews were a much more informal style. You'd meet the team, get asked some basic technical questions, they'd take you to lunch, etc. If you had some sort of recommendation (inside referral) it was even more informal.

2010-ish is when I first encountered the "code on a whiteboard", and later "code in a shared doc" style of interview. One was basically 5 hours non-stop. Pure hell.