I think the $55 fare I saw at that site did mention that it included a $2.50 airport surcharge. So yeah, leaving from the hotel should save you that plus any reduced distance costs.

If the OP of that question is traveling with others (not just alone), the taxi may end up being more cost competetive, as Supershuttle et al. charge per person. If the first person in a party is $20 and the second and third are $10 each, well, then it's only another $10 for the comfort and speed of a cab.

Note that the taxi cost will go up if traffic on the 405 is stop and go, as the taxi meter will start charging for time when the cab isn't moving. Better to do this shuffle outside of commute hours.