I'm currently in the process of applying at Facebook (which I guess qualifies as a TrendCo that recently transitioned to BigCo). I haven't even got to the technical phone screen yet, but the recruiter tried to get me to attend an "interview prep session" and then sent me a pair of videos from it totalling 2.5 hours when I couldn't, which of course I felt obligated to watch on the assumption that all the other candidates will have.
Ridiculous enough. Then there's the content. The videos are a presentation by Gayle McDowell, the author of Cracking the Coding Interview. Lots of tips about interviewing, 95% of which were pretty obvious but most of which seemed useful enough, on the assumption that the process is a given. But McDowell would repeatedly say things like "most interviewers won't expect you to write perfect syntax on a whiteboard, but some will" as if this was perfectly reasonable. And she gave "if you're writing in Python, it's a red flag if you use ++ (instead of += 1)" as an example of something she cares about herself! So both the recruiter and McDowell recommended doing a number of pen-and-paper practice coding problems before your interview, specifically on the basis that this is something you never do in your day job.
If I want to be charitable, this is Facebook trying to even out some of the biases introduced by their (apparently unchangeable) whiteboard algo puzzle interview questions, by ensuring everyone is prepared.
If I want to be less charitable, the demand for hours and hours of preparation is just (further) hazing to prove dedication.
In either case, I think this evidence that BigCos are not necessarily any more rational about hiring.