Problem with Success is

This week's number one album is Evanescence's "Evanescence" selling 127k units. Their last number one album, "An Open Door," sold 441k units. That's a big drop.
The problem with success is that people expect you to have it all the time. However, when you don't have it often (because you're either hit or miss or because you take time off in between your successes), no one seems to notice if your success drops off. With Evanescence, there's not much discussion about how little they sold this time as compared to last time.
Unfortunately, not all artists get that sort of treatment. For instance, when Britney Spears' 2007 album "Blackout" debuted with just over 200k units sold, people jumped all over her saying she was washed up and her career was over. Then, when "Femme Fatale" debuted this year with even smaller sales than "Blackout," people were quick to bemoan that Britney should retire, that clearly people don't care about her any more.
If it's not clear with Evanescence's album sales that the music business is down, then look at the fact that Adele's "21" is on pace to outsell the next two highest selling albums, Lady Gaga's "Born This Way" and Lil Wayne's "The Carter IV." Instead, with Britney, people look at her past successes and assume every album she releases should sell 500k units the first week.
People (that includes the media and regular folk) can't seem to understand that even Britney is affected by the economy. In 2002, Justin Timberlake's debut solo album "Justified" sold over 400k units in its first week and debuted at #2. Today, he would have crushed the competition with those numbers Clearly, times have changed.
Sure, Lady Gaga and Taylor Swift have sold big numbers in the past year. But they're relatively new. "Born This Way" was only Gaga's second full length album and "Speak Now" was Taylor's third. "Femme Fatale" was Britney's seventh full length studio album.
Any dip in sales for Britney is due to the music business being in or near the toilet, as evidenced by the fact that this year she's had two #1s, a #3 and another top 10 hit. Clearly, she's still having success. It's just unfortunate that more people are interested in her declining sales.