definitely. i have the standard drawbar and there's no way that would fit on mine. that's why i went the drop-down bar on the back.
the bonus with that, is that when we're overnighting we can just simply pull out the pin and it folds down so we can drop the rear bed, and then simply lift it up the next day, no mucking around with pulling the bikes off and on for an overnighter. pretty sure the ISI carrier is not that handy.
I think he does sell a bracket for a standard A frame (they are a different angle hence you need to state it on the order). Wrt pulling a pin and folding - ISI does that easily (but it is heavy with 4 bikes). Honestly at < 20 secs per bike on or off it's easier to take them off and put them back on the next day.
@Brougham - You are correct - I doubt you could drop it with both the bikes on and the car attached if it wee on the draw bar. You can mount the ISI to a rear receiver (as per what you have done) and it would drop fine.
Personally I have no issue removing the bikes as it is seriously quick and almost effortless - you wouldn't believe it until you saw it. The only effort is lifting the bike and you can even reduce that by removing the uprights - 1 simple thumb screw (in fact it probably doesn't take any longer - if you remove the upright than the hook that holds the bike doesn't need to be removed).
I have never stayed without unhitching the car anyway.
So I guess it comes down to personal preference, budget and needs as to which way to go.
I would trust the ISI on the draw bar over any bike carrier mounted on the rear every day of the week, but draw backs are added towball weight of the carrier/bikes and cost.