Not necessarily. I ran a 1.5ohm atty on my 900mAh eGo, and always stick it on the charger before it's totally dead (you can tell by the slight performance drop). Some people so have problems, but more don't. Generally, the higher mAh you're working with the easier it is on the battery. But all the same, none of these standard devices are truly built to deal with anything under 2.5ohm's.
2.0ohm's will be less stressful probably. I like to keep things as simple as possible, which is why I still have a solid state MP3 player I guess, ha ha. The fewer pieces involved, the less can go wrong.
But, adapter failure isn't particularly common, and there aren't any 1.5ohm cartos as far as I'm aware. So yeah, a Kr808 with an adapter and a 2.0ohm carto is probably your best bet then.
If you do move to mods, go for a variable voltage. As far as I'm aware, they just don't make them in the 4v range.