I wouldn't say it's a matter of a short attention span for most people as I would call it a short interest span. Losing interest in something quickly or not being able to become interested in it at all, isn't the same as having a short attention span.
There is also the issue with losing focus, which isn't the same as a short attention or interest span.
Some people's writing style can cause readers to lose focus too easily. In particular, people that write incredibly long paragraphs that ramble on & on. If they got to the point and said what they had to say with less nonsense filler text and broke it up with some white space, it would be a lot easier to read and keep focus.
Also shoving too many topics into an article, that would be better broken up into multiple articles can cause one to lose interest.
But these are issues with readability and rest on the author and have not much to do with the reader.
Now going back to the attention span issue, one of the biggest problems I have developed over the years is the ability to stay interested in a television program long enough to survive through the commercial breaks. As soon as one hits, my interest turns off and I wander away, fully intending to come back when the commercials are over...then something else grabs my attention (and interest) and I forget all about whatever I was watching and never return to finish.
This is one of the factors that contributed to me giving up TV permanently. After a few years of not watching, I found I really can't any more. Take the commercials out, and I can.
I suppose if I were reading a book and was forced to put it down and do something else for 3 minutes after every chapter, I might have the same issue with reading, too.
As far as the claims that teens don't like to read, I think they are wrong. Teens will spend a great deal of time reading about topics they are interested in, and will even read quite long articles that are well written and with good style.
What they don't like is reading something they are not interested in. Boring text turns them off no matter what length it is, and what constitutes as boring differs from person to person. I don't think age really has anything to do with it, though.
And I think housetier is right about that article having more to do with marketing than anything else. I think it could probably be summed up as this:
When selling magazines door to door, get to the point and ask if they would like to buy a magazine as quickly as possible. Don't spend 3 hours trying to make small talk with boring unrelated topics before finally getting to the point of why you interrupted their life by knocking on their door. That way they can tell you "No" (or buy a magazine) a whole lot sooner and you can hit the next house, without each potential customer getting turned off by your style & personality, slamming the door in your face before you even begin to give them the sales pitch.
And when giving your sales pitch, don't jump up & down like a wild animal or scream at them. Don't talk to fast or too slow. Don't try to sell them a million things at once. Don't wave things close to their face. Let them take a look at what you are trying to sell them.
Don't make them stand on one foot, perform circus tricks, or play Simon Says while you are giving your sales pitch or when they are in the process of making an order.
Answer their questions, explain things that are not clear, help them understand.
And if you give them a fun free gift as a reward for putting up with you, they won't be likely to slam the door in your face so fast when you come back again.
And after the sale, make sure they can communicate with you if they need to.
Don't make them swear to keep your product a secret if they are happy with it. Let them tell their friends and family and give them a way to notify you that their friends would like you to visit their house, next.
Same rules for websites.
One final note: The reason why most people like the interactive features mentioned in the article is because we all like to think that our thoughts, opinions, and experiences matter and that someone is genuinely interested in them. (doesn't matter what age you are)