Wrong, you pay $10 for the ToDo app.
Also, from what I can see of the screenshots, ToDo isn't location aware, doesn't allow for "tags", and most importantly has no "alert" type functionality. With RTM, you can setup reminder alerts for upcoming tasks that are coming due via email, IM (AIM, Yahoo, MSN, etc), phone sms text message, or via twitter. You can also receive a list of upcoming tasks daily which i believe ToDo does as well
You are trying the same argument that others who were too cheap to pay for beejive tried. You ultimately get what you pay for and if you want to pay less then you will receive less. That is the case with ToDo. It simply doesn't seem as "full featured" as the RTM native iphone app (of course i'm basing this on the ToDo app description and screenshots). If you want the best, then i suggest you use the RTM iphone app with the RTM pro account.