I believe that if a recipe is sufficiently "standardized" such that it is practically a question on preparation, it should be considered on topic. For anything complex enough to have many different recipes, it is too difficult to manage effectively.
For example, the rules for making Hollandaise sauce or choux pastry are pretty specific. It's really not a subjective question. On the other hand, a question asking for Ragù recipes is pretty useless, since everybody and their brother has got one.
I realize that there's a gaping gray area here, but just like we've all experienced on the original Trilogy (think career development), discussions of on/off-topic-ness are rarely black and white, no matter how much some of us would like them to be. Everybody needs to use his/her better judgment to determine whether a "recipe" style question can be answered succinctly and objectively or whether it's just inviting anyone and everyone to post their "favourite."
In the future, if and when the site gains sufficient popularity, we might want to revisit this decision. A central "topic" for an individual class of recipes with the most-loved ones floating to the top, complete with comments and the ability to communicate directly with the recipe-poster, could actually add a huge amount of value to a site like this. But we're not ready for it yet; if allowed, those questions would dwarf the more "concrete" questions at this primitive stage and could kill the site before it has a chance to mature. So let's try to keep them to a minimum at least for now.