Why Does One URL Direct Work And The Other Not

I read a beginners book on js and now I'm working through a cookbook style book to get a hang of things, I came across an example for redirecting URLs in the book that didn't work:

<form>
<input type="text" name="url">
<input type="button" value="Go" onClick="location.href=this.form.url.value">
</form>

After searching on the net I found another that works perfectly but I don't understand why the one in the book doesn't work.

works:

<form name="openlocation">
<input type="text" name="href">
<input type="button" value="Go" onClick="location.href=document.openlocation.href.value;; ">
</form>

I tried replacing the url with href and other tweaks, is it that you cant use ".this" here, making it necesary to name the form?