application/octet-stream considered unsafe

I get various emails, often bills from organizations that I have accounts with in PDF. Some of them send them to me as application/octet-stream, with a .PDF extension. When I double click on this attachment, it saves-to-disk.

When they send me text/pdf format, then I start acroread and/or gpdf, and I can see their PDF. This is what I reply to them with:

In the past a number of popular mail programs have resorted to looking at the file extensions to determine the file type. These same systems are very vulnerable to trojans and virii, and the reliance of file extensions causes confusion to users --- they wind up authorizing dangerous operations. It's kind of like letting your toddler play with a loaded gun. Something bad is going to happen. In this case, something bad happens to the tune of nearly $6B/year. This is despite massive spending on mostly ineffective virus scanners --- always keeping us safe from last years' attack, but never defending against what might come tomorrow. Internet standard email, as defined by RFC2822 and a great number of other documents on MIME, does not use extensions. This means that it is not possible to mis-represent file content to users --- if the file appears to be a safe picture, it will always be displayed as a picture, not a trojan. You have sent me files of type application/octet-stream. I may be able to guess that they are safe, but I have no real assurance of what they really contain.