The cult of Wicked is much larger than the cult of Rock of Ages (by virtue of Wicked being a big success and Rock of Ages not in the same league). I don't think revealing who will be in the new cast for Rock of Ages will make one jot of a difference to ticket sales, particularly if no stars are going in this time round (Tim Howar and Ross Hunter are not names that shift tickets), whereas the news about Louise Dearman is likely to have more of an impact.
I don't know when ROA's cast change actually is, but I would presume the current cast had a deadline to renew their contracts by (if the team wanted them to stay on) that has long passed.
The Equity minimum at the Duchess is still nearly £500 a week (around £25k a year) - not a huge amount for an actor when factoring in the £2,500 a year to the agent from that, classes etc. but hardly poverty. I wouldn't have thought "physically living" would be a problem.