You could just as easily ask why Mantle fans keep posting speculation again and again, with no hard numbers to refer to. Actually, just like in the console thread a few months ago, each new round of speculation seems to escalate to even higher levels. We have gone from predicting 30% or less improvement to specualting that 1ghz craptops will run BF4. Bottom line is just like in the console thread, nobody really knows.
If AMD/Mantle fans have the right to keep posting speculation on how huge the improvements will be, dont others have the right to post their own speculation that it will not be that much?