However, the sole entertainment value that comes from these on line scratch games is so limited, that you would have to have a seriously dull life to find them enjoyable.
At least in most forms of gambling you feel you have an element of control (despite the odds). Whether it's choosing to bluff in poker, choose a team in sports or 'collect' early on a fruit machine.
The difference with the online scratch card is that it shows a fake level of interaction to the user, which makes them believe they could have effected the result by scratching a different panel.
Combining this with the 'near miss' psychological effect, it will probably leave the typical demographic playing it coming back for more.