Allocation of parking stands and other aerodrome services will be by agreement between the airline in question and the airport operator.
Aer Arann for example may not wish to pay the cost of using an air bridge for an ATR service.
Consider too the type of equipment available - The specific Air bridge may not be able to extend far and low enough for an ATR.
There is also the issue of capacity. No airport operator in their right mind wants as ATR parked on a stand marked out for a 747, when they could park 2 ATR's on the same amount of remote tarmac.
Facilities such as De-Iceing can be provided by airlines themselves, ground handling companies or by the airport authority, depending on each individual airport, but you will almost always find that anywhere a 'priority' list exists it is only because that customer has a larger or more valuable contract with the company providing De-Icing.
" He who pays most gets best soonest service" as I was once told in Hong Kong...