I'll take KevinJ's "middle road" on this one as well. The abrupt stop is indeed a known issue, and can make the tractor uncomfortable to drive, but there are things that the OP can do to make it better.
When I have the front end loader and box blade on by BX, I appreciate the tractor's ability to stop quickly, and the extra weight dampens the response. When I take the implements off in order to mow, a good jerk or two reminds me that I need to be cognizant of the issue, and I feather the pedal.
I'd be interested in seeing how fast a 60 series stops when backing up while weighted down with a bunch of implements. Now this is absolute conjecture here, but it would appear to me that tuning a tranny for a compact tractor has to be harder than a larger one. A large tractor's weight changes by a much smaller percentage with implements on versus implements off. Does this make the tuning of the small tranny difficult?
BXxx60 owners - Does the tractor drift much when it's heavy, and you take your foot off the pedal in reverse? Any noticable difference with the implements off?
Manonthehill, you should tell the dealer you want to try weights. This will help balance the tractor, making it much safer for your wife and kid, and will help dampen the behavior. If you like them, maybe he'll give them to you for free?
Jesse