You're absolutely right. In fact, what ideally should be used is not checkboxes but <select> elements eg:

<select name='vote_XXXXX'>
   <option value='' selected='selected'></option>
   <option value='1'>++</option>
   <option value='-1'>--</option>
</select></option>
[download]

...which would have the minor extra quirk that the resultant form argument would be passed to the script even if nothing had been selected, but it would get the job done. And lynx is absolutely fine with handling <select>s.

Note: In the above example, I've used "" rather than '0', as "" (the empty string) can usually be considered to be (effectively) undefined, in the context of HTTP form contents.