Grandma, open the email I sent you and click the link [or] Grandma, Go to "tinyurl.com/5yp7q".

versus,

Grandma, download Skype, find it, run it, walk through the Installer, make an account, login, add my username, then call me. (and even then, this is glossing over a gross number of details that are hard for the unsavvy).

Even if it's already set up, there's no barrier to use of a simple WebRTC-based service assuming it's done correctly.

So it's just ring ring "hello?"

Vs. sending an email to tell her to click this link so that you can call her....

If she knows to wake the computer up (or start it up) during your evening hours, that's enough -- Skype starts when the computer starts, unlike a browser.

Skype is easier than email, generally (and Grandma may not bother with email...). You don't even need typing skills. Just click the "answer" button when it rings, or if you want to call me, click my name then click "call".

Then my father, became computer geek late in his years, and I can't even stop his mouth when comes to applications :) - He's bigger kid than me in that respect...

Granted, I agree with the grandparent here: ultimately, browser-based software would be easier, but you have an entrenched user base who aren't likely to quickly change to new tech.