No it's not. An empty alt specifies that it's a presentational image. On the other hand, no alt is unhelpful, as you can't tell if the omission was intentional, or the developer is just lazy.
An empty alt can also just mean "I used a tool to generate this and didn't fill out the alt field" or "I just want this page to validate and still don't care".
Making the alt tag required won't make lazy developers/content providers any less lazy, so requiring it actually weakens the signal you're looking for.
Is it better that the lazy developer is forced to insert empty alt="" to get the site to validate? Your argument is actually in favor of an optional alt tag. Allowing for a missing alt tag means you CAN tell the difference between an intentional empty alt, or a lazy developer missing the tag.
Allowing for a missing alt tag means developers don't even have to consider providing alt info, which is a terrible idea. At least this way they have to put something there, even if it's blank.
How is it better that every single image on a page has alt="image" or alt="asdfasdf", instead of a missing alt-tag?
If the alt tag was recommended - but optional - then a missing alt-tag tells you the developer didn't think about it (and who knows if the image is significant), while a present but empty alt-tag indicates the image really is decorative/insignificant.
As long as the alt-tag is required, a valid site will contain alt="" all over the place, and you can't know whether that's because the site developer was lazy (but was using validating tools) or if the site developer decided to flag those images insignificant.
Am I feeding a troll here?
(edit: It's like the difference between an SQL NULL and an empty string.)
