I'm still learning the 4e system, and I'm trying to find out what happened to scrolls. I loved scrolls back in my 1e days because it let players experiment with spells they normally wouldn't want to memorize or were not available to them. They also made a great addition to treasure without having a permanent impact on the game. Are rituals supposed to fill this role? I haven't ever seen a player try to cast a ritual.
The rules allow for consumable items, and magic items, so single-shot items you call "scrolls" could be allowed. I know I'm planning on having them - even if I have to house rule them. Each would be either a single-use ritual scroll (mentioned explicitly on page 134 of the Rules Compendium, or page 298 of the PHB) or a consumable magic item-scroll which is equal to a daily-use power at either a higher level of mastery and/or from a different class. More importantly, I'm creating consumable magic items with effects that aren't currently in existing powers.
I've had many an AD&D game session take an amazing turn - like when when the cleric is incapacitated, the party is on the ropes, but the fighter whips out a scroll of Healing God's Blessing (something I made up). I'm not giving up that ability for players to surprise me and especially my monsters.
Largely the old scroll system from 3.5 and 2.0 is gone.
Rituals are basically like any non-combat spell/effect that takes longer than a round to cast. Ritual scrolls are what's left of the old scroll system. Their usage seems to vary on the type of players and DM involved, since they are in the gray area outside of combat/skill check activities.
Scrolls for getting more spell variety for combat are gone, because D&D 4e character creation is about making choices and having limited power.
All classes are created equal and balanced one against the others. This does not mean that a PVP encounter between single characters would be balanced, but a PVP between parties might (if both parties have the same optimization level). Everyone is supposed to shine in its own role and leave other people shine as well.
The variety of available powers is part of this balance, at least combat-wise. Classes just don't get the chance to spend some resources in advance in order to have a higher number of encounter or daily powers later. Some magic items do similar things, but they are limited in what they can do. In the first batch of 4e books, when item-generated powers had a number of daily slots based on character level, this mindset was painstakingly clear. Now that items are only limited by their rarity, I feel like some of the original intent has been lost (the Essentials line, after all, was an attempt to regain some of the D&D 3.X editions audience, breaking the AEDU model and reworking this item thing).
Scrolls as you know them still exist for rituals, i.e. out-of-combat spells that (at least at the beginning of the game) had no effects on combat.