Interested? Here are the step by step guide on how to create such gadget:
1. Login to Blogger.com,
2. Visit you dashboard >> layout >> page elements.
3. Click "Add a Gadget", choose HTML/JavaScript.
4. Paste these codes there, change the bold ones with your blog address:
<script style="text/javascript">
function numberOfPosts(json) {
document.write('Total Posts: <b>' + json.feed.openSearch$totalResults.$t + '</b><br>');
}
function numberOfComments(json) {
document.write('Total Comments: <b>' + json.feed.openSearch$totalResults.$t + '</b><br>');
}
</script>
<font color="blue">
<script src="http://your-blog-name.blogspot.com/feeds/posts/default?alt=json-in-script&callback=numberOfPosts"></script>
<script src="http://your-blog-name.blogspot.com/feeds/comments/default?alt=json-in-script&callback=numberOfComments"></script>
</font>
5. Save and done.
Visit your blog to check the counts. If you are quite savvy with JavaScripts, feel free to customize it. Let me know if your need further assistance.