As long as PS3 sells 40 million consoles, despite losing Sony billions, the company going bankrupt, and the console only having a terrible software lineup, it's a success.
No sorry. As long as it sells 40 million, when XB360 and Wii sell 120 million each, it's a success, despite the devs not bothering to develop software for it and all the good games coming out for other platforms.
Um...
You know, you've elliminated all rational measures of success from your question! It's like asking 'How many games must Woking FC win for you to call them a success Disregard whether they get relegated or lose money and have to close down, etc.' Or even 'How tall must a person be to be considered a success. Disregard how wealthy they are, healthy, nice, happy, how many friends they have, etc.'
For PS3 to be a success, it has to earn Sony a profit, provide a great service to its customers, attract the variety of games and applications needed, and make up a substantial percentage of the overall console market in order to attract developer support. Number of units has sod-all to do with it, to be frank. I've always scratched my head when people have called GC a failure, when it worked well for Nintendo, made them money, and gave owners the games they wanted.