I think it is much more complicated to have a remote checkout and a download area for your customers. The main problem is that if you want to deliver an item that the custom has paid for you should only do so after you have confirmed the status of the transaction. Just because a user goes through the Payments Standard and gets back to your site does not mean that the payment was successful. It only means that the transaction was submitted. If you give out a download link at this point you could potentially be giving it to someone that did not pay for it.
With Payments Standard using a form that posts to PayPal you will only know the status of the transaction after the IPN is sent. If you can't know the status while the user is on the site you would need to have the user come back to the site, and if you do not have a login then how do you know who the user is and what file they should have access to?
If you would like to have a download center I would suggest that you make use of Payments Pro or at least Express Checkout since with both of these you know the status of the transaction at the time. This way you could have a user complete the transaction then go directly to the download page to get their purchase.
