Hi there, it's correct that Blogger permalinks are rewritten after import into WordPress so that many of your links from search engines and other sites will continue to work.
While Blogger post links end in .html, and don't include a day value as part of the link, these differences are processed behind the scenes so that most Blogger links will continue to work anyway.
However, if the link text (the "slug") on a Blogger post was manually edited, or in some other way isn't an exact match with the post title, the permalinks generated at WordPress.com won't quite work. There are also some other slight differences -- for example, Blogger automatically drops words like "the" from the permalink, while WordPress.com keeps them.
We've added to our enhancement list a feature to match Blogger's permalinks exactly on import, to help retain the permalinks a member has built history with.
For now, we recommend manually editing the slugs on the posts that you received 404 alerts for. The slug is the last part of the link, usually made up of the words in your post title, separated by hyphens. You can manually edit this in the Edit Post screen of each post, or use Quick Edit in the All Posts screen, as follows:
1. Go to the Post -> All Posts page in your dashboard.
2. Hover your mouse over the title of a post that you have a 404 report for.
3. Click the "Quick Edit" link that appears under the post title.
4. Edit the post slug to match the slug that appears in the 404 report (leave off the '.html')
5. Click the blue Update button.
You can read more about Quick Edit here:
If it's helpful, note that you can sort your posts into alphabetical order by clicking the Title button at the top of the list of Posts.