Why can't I use SIRI and dictation on my iPad2 with release 6.1?

Siri requires at least an iPad 3.

Here's an explanation of what features require which hardware.

iOS 6: Which software features does my iPhone, iPad, or iPod touch support?

Siri is not available on iPad 2. Take a look at sberman link.

It's hardware (model) and not software (ios) that determined features.

The iPad 2 will never have Siri no matter how many more software updates Apple releases for it. The iPad 2 does not have the noise canceling chip needed in order for Siri to function which means the hardware lacks the capability of using Siri so it has nothing to do with software at all.