It's considerably easier (IMO) to get started in web development than in iOS development. Web development has a fairly gentle learning curve and I personally know a bunch of people that started their careers hacking in php. iOS development has a gentle learning curve if you already know C, which even some CompSci graduates don't nowadays.
I don't think this was intended as a put down, it's just a fact that there are a ton of ways to put together a simple web app and some of them are very accessible.
A Web App is more than HTML and PHP of course. There is an entire "stack" and if you're doing it all yourself you need to know something about all of it. You will probably find yourself needing to be at least somewhat proficient in: HTML, CSS, JavaScript, PHP/Ruby/Python or similar, Apache or IIS administration, Linux/BSD/Windows administration, MySQL/Postgres/SQL Server administration, some dialect of SQL itself, etc.
I'm not sure how that compares to iOS but my hunch is that you can pretty much confine yourself to learning XCode and the framework. The water may be a bit deeper right at first than just tinkering with HTML or PHP, but the overall domain appears to be more limited, at least so it appears to me (I have not done any mobile development yet).
My last iOS app required the knowledge of Objective-C, the frameworks, HTML, CSS, & Javascript (because that's actually how you do formatted text, and javascript for event handling within that text), SQL for the local storage, PHP & MySQL for the server-side storage, etc.
I'm not saying either is harder, I think that's a fight for cats, but I did want to inform to your hunch from experience.
I think both web development and iOS development require the use of tools and languages that many don't know about at the start, as I'm sure plenty of people think, "Oh I just have to learn HTML & Javascript" and then find all of the things you've listed.
> because that's actually how you do formatted text, and javascript for event handling within that text
I would say that CoreText is the preferred way to do it. WebKit is pretty slow by comparison and leaves you with much less control over your renders. It's not a horrible solution if you are trying to share assets with other platforms though.
I don't think this was intended as a put down, it's just a fact that there are a ton of ways to put together a simple web app and some of them are very accessible.