Is it really common practice now to have laid off workers escorted out by security?
Depends on location. In the US, it's extremely common, potentially due to their more violent nature and the second amendment.
In a lot other countries, layoffs can take different schemes - they may provide notice of layoff - as in you're going to get a severance and all that, but it's a 2-week notice, and no, they're not going to buy you out, you're going to work those two weeks. Seems incredible, but a lot of companies do it because they want an orderly transition, and they do trust their employees enough to not be burning bridges. Some even go out of their way to help them find a new job (instead of just giving them the number of the employment agency) - and that includes counseling services. Heck, even benefits often continue for a few months after the layoffs (health insurance).
I don't know what it is about the US - perhaps their proclivity towards violence leads to basically shoving them out the door after the meeting is over - if you need any personal belongings, they'll fetch it for you and pack up the rest of your stuff.