Today, when I printed my book wrappers, all printed as "8 oz First Class Mail CommercialBase Price."  What happened to media mail rate?

It prints whatever is the cheapest rate for that weight.

In my experience printing wrappers anything over 7oz went media mail.  I just checked prices on the USPS website and it has 1 lb media at $2.41 and a first class 8 oz package at $2.56.

I'm not sure what the commercial part is about.  How much was the postage?

This chart show the media male rates, and both the regular first class rate and discounted electronic postage rate:

Current Media mail and First Class Parcel postal rates

for a printable version of this page, click this: Current Postal Rates

Current USPS Media Mail rates*:
  Effective April 17, 2011

To see the full list of Media Mail Rates at USPS, go here.

Up to 1 pound.......................................$2.41
More than 1 pound, less than 2 pounds....... 2.82
More than 2 pounds, less than 3 pounds..... 3.23
More than 3 pounds, less than 4 pounds..... 3.64
More than 4 pounds, less than 5 pounds.....4.05
More than 5 pounds, less than 6 pounds.....4.46
More than 6 pounds, less than 7 pounds.....4.87
More than 7 pounds, less than 8 pounds.....5.26
More than 8 pounds, less than 9 pounds..... 5.65
More than 9 pounds, less than 10 pounds....6.04

Rates in blue are the most common postage rates for single-book shipments.

Current  USPS First-Class Parcel rates:
Effective April 17, 2011
*Note USPS discount for printing First Class postage!

Not over 1 ounce..............................$1.71...1.56 with Printable Postage
Not over 2 ounces..............................1.71...1.56 with Printable Postage
Not over 3 ounces..............................1.71...1.56 with Printable Postage
Not over 4 ounces..............................1.88...1.73 with Printable Postage
Not over 5 ounces..............................2.05...1.90 with Printable Postage
Not over 6 ounces..............................2.22...2.07 with Printable Postage
Not over 7 ounces..............................2.39...2.24 with Printable Postage
Not over 8 ounces..............................2.56
Not over 9 ounces..............................2.73
Not over 10 ounces...........................2.90
Not over 11 ounces............................3.07
Not over 12 ounces............................3.24
Not over 13 ounces............................3.41

I didn't see those discounted rates when I checked.  Probably looked in the wrong section on the USPS website....Sorry, clicked the link and looks like that is from PBS, I only checked USPS site and didn't see it.  However, her book was 8 oz.  According to the chart with the discounted rates an 8oz book is still cheaper to send media mail.

I just sent an 8oz book myself, and the discounted printable postage rate for first class 8oz is now $2.41, the exact same as 1lb media mail. That list of first class postage should be updated to include the discounted rate for 8oz, because that's what the printable postage uses. I was confused at first as well, since in the past before the rate changes it did switch over from first class to media mail after 7oz, but now it switches after 8oz.

The information is not very well publicized on the USPS web page, but it's there.

http://pe.usps.com/text/dmm300/Notice123.htm

Look under First Class Mail, Commercial Base Parcels

the 4th column (Mixed ADC/ Single Piece)

8oz with the 15cent discount for online postage would be $2.41, the same cost as 1lb media mail.

Given they are the same price, the site's postage server opted for First Class.

This went into effect on April 17, 2011