Hey, I noticed that no one has answered your question yet, so I thought I'd take a crack at it.
You'll likely want to add your Analytics tracking script to all of these pages. If you don't, some event hits might not be recorded. Depending on how you're tracking your forms, choosing not to include it on all pages might also prevent your form submission goal from firing (if you're using destination goal tracking in Analytics, for example).
The only reason that you wouldn't want a script to run on all three is if you want specific functionality on one set of pages that you wouldn't want on another set of pages. For example, AdWords conversion tracking tags are conventionally added to your site's confirmation page(s). You would not want to include this code on your main landing page, as it would cause the AdWords conversion tracking tag to fire any time someone landed on any of your main pages, giving you a very skewed set of conversion data.