It's not unusual to have some updates waiting when you get a new device. It's possible it got packaged months ago. Yes, it looks like you checked for updates, and one might have expected those to appear right away, but maybe the update server wasn't available at that time, or was feeling otherwise disinclined to push the update.
One place to check is the Updates page:
http://www.amazon.com/gp/help/custom...deId=200529680
And compare that with what it shows in Device Options.
It appears my own Fire tablet (HD6) does not have the latest update, even though I have pushed the CHECK NOW buton. Device says it has 5.1.1, but the updates page shows 5.1.2.1. And Silk does not have the features you mention. Might try a manual update.