I'm no longer in Singapore, having left at the end of 2012, and I lived in a semi-D for 8 years in Watten Estates. The majority of our friends lived in
condos, a few in HDB flats.
We chose a semi-D for a few reasons. First, we left our home in Texas, with nearly a half acre of yard, and we wanted some kind of outdoor space that would permit us to lounge, eat outdoors, etc, and virtually no
condo in Singapore has any kind of large size balcony or veranda to really permit such activities... mostly a couple of chairs and a round table. Although our yard in Singapore was small, it worked very well, giving my wife the opportunity to garden, which she loves to do. Also had lots of birds and other wildlife.
Second, we like to grill a lot outdoors and in most condos there are restrictions (never mind the space restrictions) in having a gas or charcoal grill on the condo premises, and we didn't want to go to use the common kitchen/grill facilities because we use the grill so often... just want to grill outside, bring the meat to the kitchen, prep the plates, and eat on the patio.
We also like the convenience of a semi-D... easy to park both car and motorcycle... no lifts or long walks in parking garages. No hassle with security gates. More open space around us with large trees and lots of greenery making for a very nice neighborhood.
Our friends who did live in condos also had their reasons. For those with children, having a pool and other recreational facilities was important. Most had already come from apartment or condo living and preferred this style of living. Some liked the security facilities. Some liked the view from the upper stories. And some liked the convenience of nearby amenities, although Greenwood Plaza was just a short walk away. Those of our friends who did live in landed properties did so for pretty much the same reason we did... a small yard, ability to cook outside, easy parking, more greenery.