For many years of RuneScape's history, some people would argue that having 99 in a skill was difficult, even you have a lot of RS Gold. They did have some good arguments. Their first point was that there is only a slight difference in ability between a person who got 99 in a skill, and a person that stopped levelling after "maxing out" a skill.
A person with only 50 mining is able to mine iron almost as well as a person that has 99. Their other point was that you would get no recognition for your hard work if you got 99 in something that didn't affect your combat level. The only skills that really need 99 to do everything in it are smithing and construction. Combat skills will affect your combat level so other people can see it. But what about cooking? fletching? Who would know that you've spent hours of your time clicking those lobsters and that fire, or that you've seen thousands of bow strings through your inventory?
Naturally, they would also argue that doing quests was equally pointless. For the most part, quests are aimed at the middle level player instead of the higher level player. Therefore, most of the rewards will not benefit the higher level. And of course, there was no recognition for it. Sure, you could get a nice cape to signify you finished a quest, but it's not as strong as other capes most of the time, and sooner or later, thousands of people have it as well, making the feeling of accomplishment go away.
Finally, Jagex decided that the unrecognised, dedicated people who actually work to get 99 in a skill or spend time completing every quest should get their well-deserved recognition. With the release of achievement capes, you can walk into a crowd and be recognized for what you have done. To show off even more, you can even use a special emote that is specifically related to your cape! Not only do they look great, but they also have a rather nice defence bonus.
SKILLCAPES, QUEST CAPES, AND HOODS
When you reach 99, you will be given a congratulatory message in your text box, a world announcement for your achievement, and some rather fancy fireworks. Get 99,000 coins, and find the cape seller for the cape that you want. When you talk to them, you will be given the option to buy the skill cape. If you do, you get the cape and a matching hood.
If instead of doing skills, you enjoy doing quests, then you can get the quest point cape. You won't get a message saying that you have completed every quest, so just go to the Wise Old Man if you have. Collecting the cape will also send out a world announcement.
When you log on after a new quest has been released, you will see a message telling you that a new quest has been released, and the cape and hood will appear in your inventory. If you do not have enough inventory space, they will try to go to your bank. If your bank happens to be full as well, the Wise Old Man will find them laying on the ground and hold them for you free of charge. You will not be able to wear the hood or the cape until after you complete the newest quest.
It is possible to buy more than 1 cape and hood set at a time, however it will still cost you 99,000 coins every time you purchase the set. A single cape and hood set can be stored on a Cape Rack in the Costume Room of a member's Player Owned House.