Could be . . . most of the time, if the mattress was worn out the box springs were shot too. Mfg's know this and build that into the design and function . . . that's why they are sold as sets.  From what I have seen in the past, box springs need to be changed with the matt. If not, the matt will not feel right or have proper support leading to premature mattress ware . . . Most mfg's will not warrent their new matts if new box springs are not purchased at the same time. The springs wear out (get weak) on the edges and centers where most of the weight is.