Having worked for a contractor at Apple twice, I can 100% vouch for the idea that a "caste" system is in place. First off, they give you badges with a silver color, and all Apple Standard employees have a colored badge. You get looked down upon by EVERYONE when they see your badge. You can't use the company facilities like gym, pool, and can't pay for your lunch via your badge like other employees. When 3rd-party vendors come in to do demos, you aren't allowed to see them. On product launch days, you don't get details on new products, and aren't allowed to say things to customers on the phone that someone next to you might be able to say just because they're an actual Apple employee. All of your calls are live monitored in real time. I've seen people say something incorrect on the phones and they will literally come over to their desk on the phones and when they hang up, tell them to pack their things and please exit the building, escorted by security.
I was in the sales department, but there were absolutely unreasonable metrics set that were borderline unattainable, even by top reps that were contractors. Contractors also have different metrics than standard employees. Also, Apple pays these staffing companies comparable to what they pay internal staff, and then those staffing companies (Volt, I'm looking at you), take almost half, and leave you with $15-$17 per hour, with no commission.
All the while, they dangle this carrot of "If you do well, Apple will hire you directly". In my two contracts of a year and a half total, I saw probably 3 people get hired out of 600 contractors that were utilized during that period.
It's a ******** way of doing business. Granted, I was young and wanted the work experience, which is why I did it. However, I would NEVER recommend it to anyone, and suggest finding gainful employment elsewhere.