Oliver here (I wrote the article, and run Silktide).
It's early days for us, so I can't speak from years of experience, but so far there are marked differences for us:
1. We have a lot more customers. Before one or two of our web designer clients could hold us ransom over a big cheque - the sort of thing we needed to make payroll. Now we'd need a mass exodus of customers for the same to happen, and usually that would be because we screwed something up (i.e. it's fair).
2. Customers now have clearer expectations. Web design customers can expect all sort of things which they consider reasonable, and don't understand why they're not (e.g. supporting a website 5 years after you built it, changing their business fundamentally mid project, expecting 'as many designs as it takes' to get right etc). I know you can and should educate your customers, but essentially you're dissatisfying them. With products, generally people pay a fixed amount to use a thing for a time. If it doesn't work, we refund them. Simpler and happier all round.
I totally agree with your last point - if you can scale it pays better. So far, the jury is out on that one for us, but let's see where it goes...