You just have to make sure that you speak relatively slowly.
Oh no!, now that could be a problem, have you ever heard how us Kiwi's talk?. I hope that the software can learn a few new words too!. People from "out of town" are constantly telling us to slow down when we speak.
Let's face it, these days if you're not young, you're old - Red Green
BTW. I should add that I've only used the "standard" versions of these programs. So, I would expect (maybe incorrectly) that if you spent the big bucks, you would get more accurate voice recognition. This is probably one of those... you get what you pay for scenarios.
The standard versions (as well as the more pricey versions) do provide for "new" words. Which, I would suspect would be particularly useful for a "non-US" English speaking user.