You're right, and I see it no longer works under V 3.3.122 either.
I know for a fact it USED to, so Yahoo have probably changed something
again.
I tried a number of times to log in, but it said "welcome guest", so I
tried AWeb, which worked. Tried V again and it logged in correctly.
Not sure if it's V not interpreting the HTML correctly, or if it's
Yahoo not complying to HTML standards.
Don't be too quick to critisise, just because Yahoo doesn't work under
Voyager, it might not necessarily be a fault of Voyager.