Definitely varies by prof--- even in the US, which on average is less laid back, I know people who have to actively hunt down their professors if they ever want to see them. They could probably take a month off and nobody would notice. Seems especially common with fairly senior tenured profs who've moved into academic politics and PR type roles: when they're spending their days in strategic-direction meetings with deans, or giving invited talks at industry events or whatever, they can sometimes forget they have a research group and some students.
Yeah - the guy I worked for was heavily involved in EU level projects. We typically had no idea which country he was in let alone whether he was supposed to be in that day/week/month.
