I'm surprised too. Delhi Palace has always been good - not superlative, but good, tasty food and the vegetarian options and biryani have always been better and more interesting than at Jackson Diner (they even served some kind of mushroom saag once!). I've not tried the buffet at Jackson Diner but I've ordered off the menu, and the bhindi masala was an oily, gloppy mess and the saag paneer very bland and average. Wasn't too impressed. Maybe I have to go back and try the JD buffet (which, I must say, isn't all that much more crowded than DP on a weekday lunch), however I do feel that JD has been dumbed down a lot.
This weekend I had a really good lunch buffet at Nanking Express. It's only available on weekends from about 12.30 to 4pm. It's a mix of your usual Indian buffet standards (butter chicken, rogan josh, etc) and some Indian-Chinese dishes such as the chilli chicken. They also have some interesting dishes on the buffet line - kurkuri bhindi (crispy okra, almost like french fries!), eggplant, Manchurian chicken, etc. And best of all, mango lassi and a choice of dessert (you pick) are included in the buffet price! I had a really good gajar halwa but you can also choose to have mango or rose ice cream and gulab jamum...
In other news, "Tandoori Palace" appears to have been replaced by its more permanent facade - can't remember the name, sounds like Tadakil Kitchen or something - but it virtually went up overnight!