Many hostels in Madrid do have those extra services you can find in a regular hotel. For instance, most hostels in Madrid offer wifi access to their customers for free whereas hotels usually charge extra (up to 14 euros / day).
I would say the main difference between a hotel and a hostel room is the size. Rooms and bathrooms are smaller than those you find in a regular hotel.
As for the hotels being wheelchair accessible, note that it's not only the elevator but also the size of the corridors, doors, bathrooms... They need to be bigger and, bathrooms, need to be specially designed .
The best tips from your favourite hostal in Madrid.
Hostal Chelo at http://www.chelo.com