I saw Singapore's some years ago- not overly impressed as it was(then) concrete(or at any rate a hard surface)) though it may have changed a lot since? I think 20 orangs is too many as I think quite a number of these must be living together which isn't natural for them. I don't think 'contact sessions' with visitors is necessarily good for the animals either. There is(or was) also something advertised as 'breakfast with an Orangutan' which sounds like a commercial venture in which one or more of the apes take part. It used to be the female 'Ah-meh'.
When did you visit? As far back as I can remember (1980s), the Singapore Zoo has displayed its orangs on a grass-covered island. There are small areas of hard ground, but they take up only a small fraction of the island. Since about 5 years ago, in addition to the island exhibit, 3 more orang exhibits have opened - 2 "free-ranging areas" and a large enclosed cage. The free-ranging areas are one of the few zoo exhibits in the world that give orangs access to live trees.
With 4 exhibits and several off-exhibit dens, the 24 or so orangs are divided into groups of no more than 6 at any time. Some research points to orangs being naturally sociable animals (save for adult males) but conditions in the wild don't allow them to congregate in large numbers.
Contact sessions have ceased since the mid-2000s. The orangs are still brought out close to the public for photo opportunities, but no physical contact is allowed.
Breakfast with Orangs has been around since the 1980s and is still offered. I agree its intent is commercial, but it doesn't harm or demean the orangs in any way. Contrary to its title, the orangs don't sit at a table and sip from teacups. They stay on a raised wooden platform next to the breakfast lounge where they consume their own food.
The gallery has several photos of the orang exhibits:
http://www.zoochat.com/40/singapore-zoo-2008-keeper-observes-his-133192/
http://www.zoochat.com/40/singapore-zoo-2008-bornean-orangutan-island-133189/
http://www.zoochat.com/40/singapore-zoo-2008-boardwalk-bornean-orangutan-133190/