That would be strange considering they have different meanings, I assume that there is some confusion over at the Vegan Society.
I don't think this is particularly clear and, as above, the phrase "as far as practical and possible" is much different than what is stated in their definition. The problem with switching to "practical and possible" is that its rather vague, how exactly does one determine what acts are practical or impractical? Wouldn't this have to be determined on an individual basis and not by some overreaching dogma? Avoiding meat, for example, is often impractical....does that mean its vegan to eat meat in such cases? In order for this to be clear, they would have to clarify what they mean by "practical", until they do so I think they are just side-stepping difficult issues. Also I don't see why just because some act, such as avoiding the flu vaccine, may raise your risk of certain diseases that they are impractical or impossible to avoid. After all, avoiding the flu vaccine is much easier than avoiding meat, dairy, etc. The only difference is that in general avoiding the vaccine has health consequences where as the latter doesn't. So the critical idea here is not in terms of what is or isn't practical or possible, but instead of what does and doesn't benefit you. I don't see how you can justify the use of animal derived medical treatments unless you agree that its okay to exploit animals so long as their is a benefit in doing so....but then you undermined veganism.