wait, you're sending from a google apps domain? From the web interface? It always just refused to send if I've tried to do that in the past, with a message explaining why. If you're sending from a different provider, gmail help claims it will bounce it back, not drop it silently, though I've never actually tried that.
In any case, not allowing specific file types as an attachment feels pretty different here, at the very least because the list of filetypes not allowed are enumerated, the refusal is explicit, and it's not due to the subject of the exe you're trying to send.
I'm sending via a non-Google SMTP server, and there's no bounce message or anything - it's just dropped. I'd argue that silently dropping any message from a known source, regardless of the contents, is wrong. I'd be ok with the -attachment- being removed if a scan shows it's a virus/trojan, but then there should be a notice to both sender and recipient.