Yes, google often limits vouchers for new accounts only. So experienced people may have no use for them and sell them to less experienced people with new accounts.

Also google is sneaky! When i did sign up for a new Adwords account I did get the voucher credit, but also had to provide a credit card for a "setup fee" not covered by the voucher. The minimum fee they could take from the credit card was $20 even though the setup fee was maybe $5. So the voucher is not as free as it may look...

- Ben