Is PCI DSS enforcement is only banking companies?

No, PCI DSS compliance may not be limited to Banking and Payment Card companies. It may be enforced for any company handling customer credit card data. You can see now, even Sony PlayStation network is attacked and data thieves have stolen a large amount of customer credit card data.

This is not to scare the companies, but to educate about customer data security. Data thefts may not stop in the near future and get restricted to only one set of companies. The thieves may shift the target one set of companies to the other set. They will look out for credit card data, irrespective of the type of company they breach. Your company should not become a victim. This is what Visa executive has to say about the recent Sony PlayStation network data breach.

Small and medium companies are not afford to take chance and go out of business. As the adage 'Prevention is better than cure' goes, be wise to prevent. Set your security policy fool proof and get it implemented. Get compliant with regulations like PCI DSS to reduce your risk of customer data theft.
ManageEngine EventLog Analyzer offers pre-built compliance reports for PCI DSS as part of the security offering to fortify your network security. Have a look at it.