Unfortunately, this is a limitation with the switch hardware, and requires the higher priced service module. The service module has specific hardware for enabling Netflow functionality, and without it, you just can't gather netflow data. This is not entirely unheard of either -- older 4500 models required an additional hardware component on the supervisor module to enable Netflow collection.
The paragraph you referenced is stating that you can use the 10G service module interfaces at either 1G or 10G speeds, and does not imply the netflow functionality exists on any of the 10G or 1G network module options.