I don't recall any great progress in cooking in Jesus' time.  Wasn't it just as possible for people to get gastroenteritis then as it would have been in the OT.

The original rules were given to a people who were wandering around in the desert.  By the time of Christ, they were living in fixed locations much as we do now.  I would be extremely surprised if their cooking practices and with it the efficacy of their cooking equipment had not improved out of sight in the intervening centuries, Martin.
Just think of the equipment you can use whilst trekking or camping (and have to carry on your own back) and what we have in most of our houses today.

That's just what occurred to me.  We say that God's rules made sense because pork goes off, but then S.Peter comes along and invents fridges....

Who is talking about refrigeration, Boudi?  We're talking about cooking facilities.  As for who was Peter to go against the rules - well, he didn't, did he.  He had to be told to do so by God in a vision - which was also a picture of who the Jewish Christians were to accept as 'clean' (acceptable as fellow believers) and who not.