It's all about money and licensing.
Hulu checks your system (tablet in this case) to see what platform you're on. This is important to them because some platforms support their DRM (Digital Rights Management, or "Copy Protection") correctly, and others do not.
It's not DISH, and in my opinion, and really not HULU either, but rather the content creators (the Netoworks/Sudios) that require that HULU enforces their rules. If HULU doesn't play by their rules, the studio's won't let them have their content.
It's the same reason that our DISH receivers all support HDCP on the HDMI outputs. It's so that the content creators can opt to enforce restrictions on the output of the box and require a compliant display to ensure that you're not making high quality copies of content that you receive over DISH. As far as I'm aware, nobody is enforcing HDCP... yet.
It seems counter productive, but that's the battle that the music, TV, and movie industries have been fighting for the last 10+ years.
-SF