Its all about margin........it costs very little extra to purchase/lease/operate a 763 over the 762, and the extra capacity of the 763 is made available to the airlines. While its true that the 762er does have a bit more range than the 763er, 767s are rarely used for very long haul routes (especially since the 777 and long-haul Airbus airliners have become available) where range becomes a major issue.
That being said, I do think that the 767-200er is a very good airplane for thin long-haul routes.......a very reasonable number of passengers, enough space for a full service international standard business class cabin and adequate cargo capacity all add up to a versatile aircraft; I fly very often between BRU
(both in businessfirst and economy) and found the 762, with its updated interior, a superior aircraft as far as comfort and CO
's employees seem to be very taken with the -200s as well. (I prefer it to the 764 now flying that route.) (As mentioned above, CO
has a different strategy with its fleet, and wanted the 762s to operate routes that could not support the 764/777 but still offer wide-body service and cargo capacity). If Boeing would add a bit more range, and make some other updates to the 762, they could have an ideal aircraft for airlines to use on unserved, thin long-haul routes through out the world.