I can understand that you probably feel that after all the work you done to create a clean and useful plugin for the community to use that you deserve some recognition for those efforts, but consider this:
1. Everyone who uses your plugin will know who you are, so you are already getting positive recognition from them.
2. No one who reads their blogs care about the "powered by" links anyway; I certainly ignore them by default. I mean, are you assuming that everyone who reads a WordPress blog also owns and moderates one, and could make use of a WordPress Backup plugin? Besides, the blogs all use themes, which were most likely not designed by you, so I don't see how a "powered by" link is effective advertising you on the average Jo's WordPress blog anyway.
3. Like it or not, the guidelines are in place for a reason. My blogs average about 8-9 plugins or more apiece. Can you imagine if there was a powered by link for each and every one of those? All those links would clutter the blog and distract from what was important in the first place: the content. The average blog reader doesn't care what plugins a blog admin uses on their blog.
4. Your true audience are the people who are using your product, in this case the WordPress Backup plugin, and by not following a very basic guideline you will establish yourself as unethical and probably get your plugin removed from the repository altogether. See in this one instance how Clindsey, who otherwise really likes your plugin, is now feeling rather negative about your product because he feels you have infringed upon his personal blog space with your advertisement without his permission? What's really "not right" here?
5. I think you'll find that if you politely give the users of your plugin the OPTION to place your link on their blog, many of them probably will. And even if they don't, you've already demonstrated your expertise to them, and they will have a positive reaction to you, your product and your company. Isn't THAT what you really want?
So please, take your time gathering your thoughts, and if you still feel that following the clearly outlined guidelines to hosting your plugin in the official repository are unfair or "not right" feel free to host them on your site instead.