Aside from physical loss (which I addressed above), losses from malware are a real threat, and they are much smaller threat on mobiles than they are on desktops (at least for the time being...). IMO newbies should be steered towards mobile wallets, especially deterministic ones, not away from them.
Exactly. The security model of mobile devices is usually much tighter than that of PCs and Macs.
For example, Android apps do not have access to one another's data by default. That is, unless:
- the device's kernel is specifically compromised to allow that (extremely unlikely),
- the device is rooted (usually impossible without explicit action from the user), or
- an app explicitly permits another app to access its data.
On a computer running a regular Windows/Linux/Mac OS X, however,
any application you download and run can access all your other applications' files, including your private keys.
Even though private keys are often encrypted, there is a trade-off between security and usability, and in practice usability often wins here. I would much rather prefer to prevent a malicious entity from accessing my keys than rely on the strength of my password (and on the absence of keyloggers).