Only those who were never aware or used tabs would say its not an important feature - once you used tabs there is no going back!
It's the exact same thing as if Firefox or Chrome removed tabs from their browsers: Suddenly being constrained to a single page at a time is neither functional nor acceptable. Sadly, I will be looking for a new notes app if tabs are no longer available in the client.
I also challenge Evernote to produce their data on tab utilization. Are they really collecting metrics on our app client's number of tabs and frequency usage? Anecdotally, all my colleagues who use Evernote always run multiple tabs.
Apparently tabs were never made available on Windows client, which naturally would skew the already questionable data on usage, but it makes no sense to match the versions by removing such a powerful feature.
You also have to wonder what's going with Evernote's leadership and decision making: I find it hard to believe no one at Evernote used tabs, and those must be just as upset about it as the rest of us, but apparently they're either not able to speak up or not being listened to. Either way, that's not a good sign for Evernote's future.