The anniversary buff was a 100% increase in legendary drop rate. The rift buff is a 100% increase in legendary drop rate (formerly 25%, as shown in OP's quote). I'd imagine this means that, when in a rift, you have a 200% increase in legendary drop rate, multiplied by the torment bonus and the magic find bonus.
I could be wrong on the 200% part, but I'm fairly confident on the other part.
Rift bonus and Torment bonus are multiplicative, so for example a T3 rift gives 152%*200% = 304% legendary drop chance, or +204% compared to normal non-rift. The table above for non rifts is correct, for rifts it should become
(see also here:http://www.reddit.com/r/diablo3/comments/26a358/new_legendary_drop_rate_chart/)
Now comes the difficult part, namely including the 100% anniversary buff. The above results are obtained using a formula like this one: