I think it is far more likely that the deficit of detail in a big enlargement would arise because of lack of detail conveyed by the lens than because the printer wouldn't manage to print any detail that was present. With the Canon 40D, the image of a correctly focused star (which should be a point) is a circle with a radius of several pixels with all the lenses I've tried ... the smallest circles are in fact given by astronomical telescopes rather than camera lenses, which are compromised by the need to cover a relatively wide angle of view. I think that lens resolutions need to at least double to cope with the imaging demands of the Canon 40D, which is "only" 10MP on an APS-C sensor, roughly the same pixel density as the 21MP full frame models.