Basically, the low paying jobs need to point out the salary range right from the get go, like on the webpage before you even submit the resume. They don't want people to "discriminate" because of the pay alone, but they need to realize that they are wasting their time and resources interviewing and processing someone who will be turned off by a poor paying job and consider moving on without accepting the job.
On the flipside, I do understand why well paying jobs, specifically anything 50k+, do not advertise their price until late into the employment process. They don't want every unqualified person submitting their resume and calling, just hoping that they can land the job.
There's nothing more annoying than a sub-50k job failing to list their pay, and then wondering why alot of people waste their time in the interview process.