I use Siri to check the weather often and I rarely check stocks using Siri. I think I have only opened those apps maybe twice since I got my iPhone 4S.
I don't use the Stock app, but I do use Siri to check the weather regularly. I only open the app to check the weather in my old home town, mostly because she has a little difficulty with way I say the city name. LOL.
Occasionlly for weather and never for stocks. y
I used Fidelity Investments and CNBCpro for Stocks -obviously not with Siri.
I use Weather Underground for weather -again not with Siri.