I haven't grown Rudbeckias although I probably should, but I've read about how seed suppliers plant fields of the same variety of flowers so that no other variety is close enough to polinate them. The article below explains some of that, and the distances pollen travels and how; whether by wind, insects, etc.

In the home garden the varieties will be closer together and more likely to cross polinate so the seed would not necessarily come true. On the other hand you might get some very interesting colors and shapes from the crosses.

Here's a thread about sowing Rudbeckias on the Winter Sowing Forum:

http://forums2.gardenweb.com/forums/load/wtrsow/msg122208208649.html

I hope this helps :-)

Here is a link that might be useful: How growers keep seeds true to type ...