Unfortunately a LOT of PR agencies assume that recipients of their press releases actually care. I suspect most don't.
Unless you're a really popular brand with a zealous following (think Apple) I suspect your press release is not going to be prioritised.
If you put all the actual content into an attachment you're making it way harder for the receiver to work out what you're contacting them about.
I'm not sure what makes a "good" press release or what makes a "bad" one, but I've had some really really bad ones over the past couple of months.
First off .. attachments ..
If you're sending a release it's going to be text. Why put it in an attachment? If it's in an attachment I'll have to open it separately .. if you put it in the body of the email I don't have to - I can read over it quickly.
Links - why on earth do people forget to include these? Why should I have to go hunting for them?
Price - if you're selling a product or service then pricing info can be pretty useful
Images - do NOT embed them in Word docs. Seriously. Also - don't go sending 10 megs of attachments to people. Just link to the damn things. If someone cares enough to download them and maybe use them you gain - plus you can actually track the downloads
Dates - if it's for an event it's kind of key to know when it is
Location - same as above
(Tip: If you can't write coherent press releases outsource it to someone who can. We use Kelly - she's awesome!)