The short answer is that steel is more durable.
To go on about it... plain aluminum sprockets are simply not acceptable. When I turned wrenches for a living, I have installed them at customers' insistence and have had them visibly worn in a month's time. When the aluminum sprocket wears, I have seen that often, the chain will prematurely wear as well. I can't explain or theorize this; it is my observation from real life customers.
Hard anodized aluminum sprockets are like hard chocolate on a soft serve ice cream cone. A hard outer coating on the sprocket delays the above.
Steel sprockets are not as critical about sprocket alignment. Some people confuse "Wheel alignment" with sprocket alignment. I personally don't care where the wheel is pointed... I want the rear sprocket to point directly up the chain. I talk about my chain alignment on my wheel change page: http://www.ducatitech.com/info/wheelchange.html
Steel sprockets shrug off neglect far better than aluminum sprockets, easily by factor of 10. When I change "chain and sprockets" on our bikes, typically between 12,000 and 15,000 miles, I will note that the sprockets show no noticeable wear. I do not know if it is acceptable to use old sprockets with new chain, so spending my own money, I put on new sprockets with new chains on our road bikes.
I consider aluminum sprockets appropriate for racing use, where the driveline is serviced at a frequency of 50~100 miles and parts are replaced without hestation or regard to price.
As for the regina chain, note that it has solid posts on the "rivet" link which requires a quad stake tool to properly peen over, while DiD has hollow ends on the posts, which is more conventional.
I am somewhat over the top when it comes to conservatism towards reliability as I'm a Ducati rider that isn't afraid to set off on a 400 mile day without hesitation or worry.