NJ,
There are people who are willing to spend the money to do their multi private, then continue on with their instrument and commercial training in a twin. I did my private in the 152, then went on to do my multi private...and even did my instrument in the multi. I'm glad I did that. All the rest of my training has been in in singles. I'm glad I did it this way, although there are many who will probably argue that you don't need to do your multi in the instrument...and there are those who will push to do all your training in a twin. I don't regret doing things in the multi, but if I could redo everything...I'd have stayed in a single. It's much cheaper. Multi time is important, but I'd rather get paid to fly a twin (MEI, etc) versus paying 210/hr for plane and instructor. But that's me.
Jenn