Please go through and compare the two pages section by section and by the end of the page I think you'll see that the design is not just inspired by Nathan's page, but an unattributed derivative work.
Some accessibility, usability, SEO and compatibility issues you might want to take a look at:
- Check out your favicon, it doesn't work in IE8, perhaps due to non-standard size, mime-type or non-ico format.
- Strip out the inline CSS.
- The Gothic font has no solid baseline in IE8. The individual letters jump up and down 2-3 px. Perhaps a Fontsquirrel issue?
- The social media buttons hug the browser toolbar. In some browsers there is just a few pixels between clicking Tweet and clicking a bookmark.
- Add alt-attributes to all images, empty if decorative. Specifying width and height will help with rendering or when the images won't load.
- Test your site with noscript. The fall-back font isn't sized properly and lacks enough line-height, so sentences overlap and lay-out breaks.
- Did you forget to style your footer? It uses the browser standard Times New Roman font for me.
- Declare (UTF-8) charset at the document level.
- <a name="foo"> for internal anchors is obsolete.
- Add spacing between links and words: "$129<span>Buy It</span>" or else without styling or for screenreaders it will read: "$129Buy it"
- If you want to support older browsers lack of PNG alpha support, simply bake your PNG's with the website background, convert to 8-bit or add PNG alpha support with javascript or .htc
- Specify canonical or make sure your site serves only one unique page per URL: non-www and www redirects, remove or add trailing slashes, "index" added to the URL's or without, use lowercase in your URL's (both uppercase and lowercase letters return the same page). A combination of the above can result in 256+ different URL's returning the same page.
- Encode spaces or replace them with dashes, for example when linking to your sample chapter PDF.
- http://www.crossbrowserbook.com/Knowledge/index renders differently in different browsers (whitespace near the end). It also lacks a header or footer, so no way to return: visitor trap. On that page a spelling error "startet".
- Consider using summary, <thead> and <tbody> for relational tables, like the browsersupport tables. No alt-attribute on the browser logo's makes this table unusable for the vision impaired.
- Facebook button is in German.
- Study your pagetitles and see if you can target them more. Consider adding the site title. Consider adding a meta description. Consider adding a sample chapter as HTML content to the website. Consider supporting Chrome Frame and future versions of IE (<meta http-equiv="X-UA-Compatible" content="IE=Edge,chrome=1" />).
The landing page looks really familiar...[1] It's fine, but next time please ask before borrowing my code and designs.
Good luck with the launch. I hope you sell a lot of copies.
-Nathan
[1] http://nathanbarry.com/app-design-handbook