If you spend a lot of time on public transport, an iPad isn't really that much of a luxury item. It's a really pragmatic choice, and at least in the UK an entry-level or recent secondhand iPad is not much more expensive than the cheapest usable alternative.
Most seats on British trains are not at tables, and while many (by no means all, depends on the operator) have a seatback tray table, it is generally not the right shape for all but the smallest laptop, and the proportions are not such that they work well with convertible PCs that use screen-cover keyboards.
We really get crammed into trains.
An iPad is large enough to read a book or emails even if you are stuck without a seat, the on-screen keyboard is practical enough to write reasonable emails or edit small documents on, watch a film on, etc.
So is a very cost effective way to make use of what might be 2+ hours of every working day.
(Train travel is pretty expensive over any distance, too. An entry level iPad is only about ten times the cost of an ad-hoc journey into London from where I am -- and that's only an hour away.)