These threads make mention of the W7DC plug:
http://www.peachparts.com/shopforum/search.php?action=showresults&searchid=757187&sortby=lastpost&sortorder=descending
The owners manual may be hard to argue with though. I don't understand the difference between it and the Bosch site? Perhaps Bosch was providing a "catch-all" gap that covered many autos using W7DC?
Newer electronic models often times idle better with a wider gap. If yours is a points & condenser setup, you might not want to venture too far off the factory recommendation.
My 2 cents.