Price difference between delivery menu vs dining @ Anjappar

Here is the attached pic showing the price difference between home delivery menu vs in store dining. In this case this is Anjappar. I am not a great fan of it due to the 'service' and the attitude.
You can see how these restaurants can deliver "free of charge" to your home. Simply hide the cost in food items and jack up the price by ~ 30%

1x Vegetable Biryani TAKEAWAY- SGD 6.50
1x Vegetable Biryani DELIVERY -  SGD 8.50

That's a 30% difference and if you are ordering for a family, you may even make a cab trip to near by location. ;)

One thing is the prices displayed are exclusive of GST. This is of an interest to me as this is supposed to be 'illegal'.

Update: About my wording 'illegal', realized that for Food items exclusion of GST is allowed and IRAS gives waiver if service charge is applicable. But I haven't seen service charges with Indian restaurants so the price should be inclusive of GST.

I still prefer Brindas for Indian food delivery.
http://srichakrak.blogspot.sg/2012/05/indian-food-delivery-in-singapore.html