Being that it takes (in many areas) 4 times the processing power to render a game at 1080p @60fps as it does to render the same game at 720p @30fps, the HD consoles could play many games at these resolutions but the graphical detail and effects would fall to a level that most gamers would associate with "Wii Quality" graphics.
When you look at most multi-platform games that have a PC version, a mid-range ($1000) PCs today are getting to the point where they can reliably render their version of these games at 1080p @60fps with higher detailed assets and somewhat better effects. With how a well designed console can get similar performance out of more modest hardware, by the end of 2010 a company could (potentially) produce a console which played games like this and sell it for $300 without losing too much money. I'm not certain that you would see original games produced for this system at 1080p though being that many developers would probably favour the higher detail and better effects possible at 720p @30fps.
