Is it really necessary to have prior SaaS experience to work for SaaS companies?

I've noticed a lot of job postings from SaaS companies asking candidates to have, "5+ years of designing SaaS products."

I've designed mostly customer facing web and mobile apps, but only a small portion of my work would be for a SaaS product. I guess I'm not sure if I'd be lacking in certain skill sets or design approaches because my limited understanding of the differences in SaaS is how the product is deployed and its pricing model.

Was hoping someone could shed some light on this for me, thanks in advance!