They didn't need to; Hotmail offered free e-mail accounts which was unheard of at the time; Gmail went viral for offering 1GB of storage which was unheard of at the time. The latter also had scarcity with its invite system, I'm not sure if that helped make it more popular or not. Definitely helped prevent it from collapsing under its own success though.
Anyway, I think any service now that shows up offering something used by many that is now paid for free will become popular on its own.