I recall that Father Kyril Jenner, in a message posted to one of the lists in the not-too-distant past, explained that the practice of commemorating both the first hierarch and the diocesan bishop at services has its origins in the time before the autocephaly of the Russian Church, when there was only one ruling bishop, the Metropolitan, who was assisted by various regional vicar bishops. When these regions became canonically established dioceses and their bishops proper ruling bishops, the long-standing practice of commemorating both simply wasn't discontinued.
This would explain why this peculiar practice—and regarding this Bishop Tikhon is quite right!—is generally observed in the broader Russian sphere of influence (which for these purposes would include, I suppose, Poles, Ukrainians and Carpatho-Russians, as well as the North American Metropolia and the Parish Exarchate, and others), but not beyond it. An exception to this is the Serbian Church in North and South America (and perhaps also in Australia?), in which all priests commemorate the Patriarch — a practice, I imagine, related to the reconciliation of the Patriarchal and Free Serbs in 1992. Liturgical books printed in Serbia, however, only call for the commemoration of one's own bishop.