Well it turns out the ESPN and Yahoo! playoff machines each have the tie game option. Still couldn't find the apparently anomalous set of circumstances that NFL.com has where GB and DAL win in Week 16 doesn't clinch for GB.

At 11-5 (only way to win in Wk 16 and not win division), they have the tie break over Dallas (conf) and Eagles (head to head). Even if you make Eagles the Division winner, can't get Dallas over the Packers for WC.

Couldn't create a tie game that helped.