It may not be just 3-4 hours difference, it could be a very significant difference in convenience. For Berlin to Munich, I'm pretty sure there's no single RE alternative, so you're probably transferring 3 or 4 times as well.

I'm sure in some cases, an RE is a bit more competitive with an ICE, but in plenty of others you're asking for a pretty unpleasant time. (And this is from someone with a Deutschland card, making RE trains "free".)