This Google web page gives you part of the solution for Embedding a spreadsheet in a blog or webpage. Unfortunately, they only talk about Google's near defunct "Sites".
The directions for blog embedding are cryptic: "If you want to embed a form in a website or blog, click the More Actions button at the top of the editor, and select the 'Embed' option from the drop-down menu." I think this language is obsolete.
Here's how you do it now. In the Publish to Web page on Google Docs there's a drop down that defaults to web page. Choose HTML to embed in a page instead. You get an iFrame tag you an put in MarsEdit HTML or in Blogger.