There are plenty of short rpgs that are 10 hours or less on normal play through without speed run.
A couple factor comes into play like
The length of Story
It depends on three big factors- cut scenes, dialog and detail. All of them are pretty self explanatory. Now a days games are loaded with cut scenes, so it's more common to find shorter games in the past. Some developer don't think a story is necessary when 90-99% of video game involves the protagonist saving the world.
Pacing
This category is based on combat system, animation sequence and experience growth rate/rare item drop rate.
In typical Japanese Rpg(JRPG), uses a slow pace combat system that is turn based. While, American Rpg uses a faster pace combat system that is more of hack and slash action rpg.
Experience or rare drop plays a big roll in speed. If a game is really easy to get uber weapons or experience, you die a lot less and beat most of bosses with relative ease. Animation is huge factor when you have to see the dam attack over and over again. Most JRPG have those fancy over-the-top attack sequences like Final Fantasy summons/limit breaks or Super Robot Taisen. In American Rpg have far less due to action rpg combat system. It's too fast pace. When you do a special attack on Western Rpg you will see a far smaller animation sequence. American programmers think attack sequence is too much fluff. Do you really need to see your character jump from the skies to grab a meteor and toss at your enemy, while dealing partial damage? No
Content
This category is based on extra missions/sidequests and town exploration(talking to town people and moving around the city).
If you have less people to talk to and ignore most extra missions or sidequest your game clock will reduce as well. It's far easier to beat a game then to complete. Some games don't even have town exploration anymore, instead they uses a point a click system. Once your enter a town you will see a menu appear which mainly consits of shop, save/load feature and talking to town people.
A few games I could name
-Final Fantasy 1(Dawn of Souls)
-Final Fantasy Crystal Chronicles: Rings of Fate
-Marvel Ultimate Alliance
-X Men Legends 1
-X Men Legends 2
-Arc the Lad 1
-threads of fate
-summoning night 1
-fable
-rhapsody
-Baldur's gate 1(very close or borderline 10 hours)
-Baludr's gate 2(very close or borderline 10 hours)
-Champions of Norrath(very close or borderline 10 hours)
-Champions of Norrath Return to Arms(very close or borderline 10 hours)
-Jade Empire
-Sudeki
-Gurumin