I know this question is quite old, however, I have successfully built many complex data entry pages without form tags. Although it isn't considered "standard" by many, it is NOT inappropriate to use inputs without a <form>
. My projects were instances where I needed complete control over how the page behaved and the default form behavior was getting in the way. Was able to perform page and field level validation ( using JS ) and "submitted" the data with Ajax calls etc...in fact, this is my preferred way these days.
Lots of JS is required, but its not that difficult and is easily done as reusable code.
There are also other instances where I def do NOT use forms with inputs such as Login Pages.
Hope this testimonial helps someone.