Oh no, P1R got into the RSS specs... ;)
You're going to find people who will consume the data in different ways. You'll have the individuals who will use either the feed or the newsletter, but sometime it will be both. Some people may click through to your site less if provided a feed, but at least they'll still be keeping track of your information.
If a site offers me a feed I'm happy. There are very few sites I take the time to visit regularly, but I can always scan my feeds and get an update on a wide variety of sites. You're making it easier for me to aggregate your info in my own way.
If you don't offer a feed, but do offer a newsletter then your site had better be quite good. I'll subscribe to an RSS feed a lot quicker than a newsletter. Newsletters are a bigger commitment for me.