The demo literally held my hand all the way through it and told me what to do... It was incredibly easy...
Its also not a complete game... I"m sure the full game will be incredibly large, much larger than any previous King's Quest Game. It will be more difficult and take more time simply because of its length, amount of dialogue and amount of puzzles.
In the early days, they only had room for a few puzzles, there was not much room for dialogue, and obviously graphics and audio were limited as well. Thus a need for artificial ways of extending gameplay. Limitations were caused by the fact computers simply were not as powerful as they are today, and they had to design games based on the limitations of their customer's systems (many customers did not even have hard-drives and were limited to floppies of various sizes).
Later on they started adding 256 color graphics which took up alot of space on floppies, so length was limited due to that reason(the games were also designed with 16 color graphics for people who didn't have expensive 256 color video cards yet).
Majority of people did not have cd's yet, or much HD space(5, 10, 20 megabyte hard drives were new and quite expensive). So games were still artificilaly lengthened by other means to justify their costs to the customers...
So if they didn't have artificial ways to extend the gameplay length, and lead your hand through the game, they could easily be completed in 1-3 hours. People were not willing to buy games that were that short back then, and would not pay $30-$60.
If the companies did not make that much per game, they lost money compared to how much they had to pay the teams, and cost of making the games. Remember even technology was expensive back then, so they had to make money to upgrade their systems or pay for systems they already had.
You literally can't compare todays powerful computers to the way things were back then. Its a completely different industry. Now designers have incredible tools to work with, and space to work with. Many people have access to machines that are powerful enough to handle it.
So yes in today's market on today's machines it would be unforgiveable to have dead-ends, on games that literally are extended simply due to dialogue, audio and visual methods. No one wants to start over on a 30+ hour dialogue extensive game, just because they missed something during the first part of the game.