I think this is likely different in the UK vs the US. From what I've seen, Salesforce Admins/Developers will be earning around the same amount as SE's over here.
The US, as always, is an outlier on salaries, however the difference between admin and dev comp in the UK does exist. Admin salary ceiling is probably about £60K, after which you are either very senior or bring a good mix of additional skills. For devs it's about £80-90K, after which you start looking into architect positions.
I think admin salaries go higher than that once they start being process driven roles rather than pure "admin" ones, which the senior ones tend to be. ie admin progressing into consultant whereas dev progresses into architect.