receive the difference in price as long as the refund request is made within 15 days after the cut in price. As a result, those who purchased the 16GB Google Nexus 7 tablet from the Google Play Store on or after October 14th will receive $50 back no later than 14 days after you make the request for the refund.
Once Google introduced the 32GB variant of the Google Nexus 7 priced at $249, the 16GB model of the 7 inch tablet was cut from $249 to $199. To request a voucher from Asus or Google, click on the appropriate sourcelink.
source: Asus, Google, The Verge via Phandroid