Where the line is in racing differs from person to person and from driver to driver. No doubt Schumacher thought what he did was acceptable, just as Rubens thought it was too much. It's an interesting conversation to have though.
There is the point to be made that these people are drivers of the highest calibre, with superb car control. It may be that while it looks like there's no room to us, Schumacher knows exactly how much space Rubens needs and gives him that and no more. That's giving him the benefit of the doubt, but given that no crash occurred I can see the argument that they're just both superbly skilled drivers right at the edge of what they can do. No problem with that.
