In my case, I didn't feel more pressure/they didn't ask me to decide any earlier. I don't think there is anything wrong with asking for more, even if you don't end up enrolling - especially if you make sure to let them know by their decision deadline (because then maybe that money that they offered you can go to someone else). As unfortunate as it is, higher ed is a business, and as an applicant/admitted student, you are the customer. So I'd say be as assertive as you can be because if you aren't someone else will be and, ultimately, the "product" you are buying is not essential - you have the power here.