I've noticed that insource:"lemonde.fr" does not function the same way on en.wp as it does on fr.wp. By default on en.wp, all namespaces are searched (meaning that to find out how many entries link to lemonde.fr requires searching twice, or going to the advanced search before searching), whereas on fr.wp namespace 0 is the default.
Is there a reason for this difference? FWIW, just searching in mainspace seems like a much more logical default behavior.