Famous or successful? You can't really compare sales from 10 years ago to sales now, album sales are so much lower nowadays so yes, they've sold less than Steps but it's not really representative of their popularity or success. Things are a lot more slower in general, Steps churned out 16 singles (including a few double A sides), in the same amount of time, The Saturdays have released 11 singles. The Saturdays haven't really gone 'global' yet either, Steps were promoting and selling their CDs worldwide.
It'd make more sense to compare them to someone around now. They're reasonably successful with nearly 3 million records sold in a year. In terms of fame, they're probably one of the biggest brands out there in the same way Steps were while they were at their peak.