Unit sales of flat-panel TVs were up 4% from a year ago in the Black Friday week. But retailers' deep discounts pushed revenue in the category down 6%, market research firm NPD Group said. The average price fell to $333, from $367 last year. Overall U.S. consumer electronics retail sales slipped 5.6% in that week, the official start of the holiday shopping season, after a 4% drop the previous year. Notebook PC sales disappointed despite a new Microsoft (MSFT) Windows 8 operating system. But Google (GOOG) Android tablet sales surged.