Yes, you are talking tosh!
Firstly flash has a wear-out mechanism, and while most uses won't see this, that is not to say it will not bite you due to the file system journalling, etc, working things through.
Secondly all electronics can fail! I have had a couple of USB flash drives die for no obvious reason.
Thirdly, all your stuff on one ipad - and some thief swipes it, or you lose it - what then?
Of course most folk don't think through the consequences of their PC/phone/ipad being lost or damaged, and so they don't have a (usable) backup to recover from. It end in tears, I can tell you...
So yes we will see flash taking over more and more, and for read-access it is amazingly fast, but not so great for random write access. And yes it is more robust than a lot of HDD, particularly in high shock/vibration environments, but it is not perfect.
So what for home back-up (and restore)? A lot might trust their data to "the cloud" but I would not, as you get no guarantee/indemnity if if fails. For example. we use Googl's 'professional' email service and their support is crap. What is your data gets hosed? Too bad sonny...
If you don;t care too much about privacy, etc, then a super-sized ipad and a cloud back-up is a great combination. But if your ipad dies, how long to sync 1TB of data back to it? And will said users have their log-in details stored on the now-dead ipad so they have to all intents and purposes lost the lot?
At least with your own backup, even on the quaint old HDD, you can get a local expert to sort things out for you.