imaleader-
If you're okay without K for P certification, that's fine. Some of us are looking for assurances. Are Splenda or Equal inherently chometz? No. However, it is important for some people (like me) to be told that a rabbi supervised the plant, and that there were no non-kosher chemicals or soaps used to clean the equipment, and that the employees of the plant did not inadvertently bring any chometz into the plant while making the K for P items.
During the year, there's a rule that if 1/60th of the vessel is non-kosher (i.e. accidentally splashing a bit of milk into a pot of chicken soup), the food in that vessel is still considered kosher. However, there is no such rule for Passover. And, to your point, Equal does have OU certification year-round. Perhaps there's an extra expense associated with Passover certification (most likely there is), or perhaps there's actually a reason that it is not certified.
As for legumes and such, no, there is no halachic reason for it. It is tradition. I was told that if you touch something with kitniyot (thanks for the explanation, Bumby) to your K for P dishes (i.e. string beans), it doesn't make them chometz, and eating them doesn't, per se, mean that you 'broke Passover'. However, tradition for many of us dictates that we don't eat it.
What defines Kosher l'Pesach? It depends. For me, everything I eat has to be heckshered. For someone else, it might just be not to eat bread. For another, it might be to eat things that aren't inherently chometz (sounds like Bumby is in this camp). Religion is a very personal thing, and, really, it's to each his/her own.
As for the baking powder and peanut oil, I did get explanations for those items at some point in my life, but I don't recall what they are at the moment. If I remember or find out, I'll post it.
If anyone is interested, the OU site has a listing of items that are certified, including a listing of things that need to specifically say K for P and those for which just the OU is fine. There are other heckshers out there for Passover, but this one is most common. http://www.ou.org/chagim/pesach/pesa...01/default.htm
Dina



Now, if only Heinz Ketchup and Hellmann's Mayo would accomodate.....