The default installation of osc is indeed outdated and simple. But, because of the vast community it has, the vast spread of the software and been so simple and fast the oscommerce can be fully customized to any kind of needs a merchant can have (in matter of design, user experience and backend programming).

Recently a valid option many like to think is magentocommerce.
For now – I would not recommend magentocommerce to my customers without warning them first. Magento is DEADLY slow and has a deadly bad documentation. The customization process takes a lot more time and of course this is translated into money – Costs of running a magento shop are a lot higher. I tend to think that magento hasn’t a good documentation just because their staff must offer expensive services to help merchants to run an open source e-commerce application…