Given that toolbar PR data is unreliable (and imprecise), this is certainly nonsense. However, even if it were true, what advantage would other search engines gain by such knowledge?
The link: command fails to work in Google for technical reasons. If they could make it work better they would.
Whether they care or not is irrelevant. The fact is that it helps webmasters determine how effiently Google is updating it index. The inescapable conclusion is that others are doing better. Of course that does not mean that others produce better search results but it does mean that there is room for improvement at Google.