The first half of the post applies to web development too. Most designers design for the 'best case' scenario and leave out all the tiny details like error conditions, interactions, too much/little content, various screen sizes and touch vs mouse interactions (hover especially).
Let's face it, nowadays unless you are designing a content site there is an immense amount of work needed to handle all the complexities of designing a web or mobile app. This is why things like Bootstrap or other frameworks are so popular, they allow a designer or developer to cover 90% of those scenarios and focus on the important things.
> This is why things like Bootstrap or other frameworks are so popular, they allow a designer or developer to cover 90% of those scenarios and focus on the important things.
You're definitely right, but this IMO this is a broken model.
Most of the times superior web apps and mobile apps are the ones with extremely well curated UX, maybe even featuring a slim UI. OFC is the product is very revolutionary, you can be still successful with trade-offs in UI/UX, but the second one is far more important than the first one, if you have a shining, super cool bootstrap template, but a horrifying UX, people will definitely walk away and never return. If you have a decent UI, but an outstanding UX, they will stay and give you suggestions (implicit and explicits) in how to improve the UI as well.
That doesn't impugn the model. Using Bootstrap to cover the 90% case, rather than building from scratch, lets you spend more time and effort on solid UX, rather than having to reinvent basic UI from the ground up.
Let's face it, nowadays unless you are designing a content site there is an immense amount of work needed to handle all the complexities of designing a web or mobile app. This is why things like Bootstrap or other frameworks are so popular, they allow a designer or developer to cover 90% of those scenarios and focus on the important things.