I think there's some mix-up of issues from your end while dealing with this topic, which is a bit rare for you.
With regard to your line "Rather than rewarding the length of service, let your boss reward the performance," there are Annual Performance Reviews and salary hikes to take care of the typical performance issues. This is supposed to exclusively focus on those with a long tenure.
And, without generalizing it, the chances of Performance reviews being more focused only on performance rather than politics or other issues clouding the reviews are much lower in Proprietary Concerns, relatively speaking, for the simple reason that here the number of layers between the employee and the Top guy (and consequently the chances of other issues coming into the decision-making process) are relatively lower than in larger Companies.
This was the reason for my suggestion about including Performance-related criteria as a 'CAN be' AND indirectly, else the employee focus is likely to move from the profit-share reward to other issues. Why give a scope for such situations at all?
In reference to your lines "While distributing profits, if you make length of service as a criterion then are you sure that they are all efficient employees?...moved long ago," I think that's an over-assumption to make of THIS Concern/Company.
Further, that's also an assumption no one can make for even MNCs or super-large Corporations. I know of many persons, at different levels, who work in Top-notch Companies, including Mega-Corporations (both IT & Non-IT), who fall into this category. They haven't moved for different reasons, surely not because they weren't efficient or confident.
And herein lies the catch, or rather two catches.
Firstly, the standard line in HR is: "A person leaves the Manager, not the Company." So not all people move from smaller Companies/Concerns to bigger ones just because they are confident or efficient.
The very fact that this Concern/Company where Mrs. Gauri M. Khan is working is even thinking of rewarding those with longstanding innings here proves that (1) the Company has cash and is doing well, (2) at least a majority of those who are working here are performers, else there wouldn't be profits to share, and (3) the Boss seems reasonably well-considered by the employees, else there wouldn't be many employees who would be long-timers.
The Second Catch is: employees who currently exhibit 'continuance commitment' may not necessarily have been so from the beginning; in fact, they wouldn't have been. The reasons why smart/efficient people slowly change to an attitude of continuance commitment don't just depend on them alone. The Organization too contributes quite a bit for such a transformation of the employee, in different ways.
A classic example of this scenario, to those following the Company for the past decade or so, would be Infosys.
For a Company that was the Bellwether of the Indian IT industry for over a decade, if not more, everyone had to see the situation of the Company slipping in almost all benchmarks & NRN having to make a brief comeback & eventually Vishal Sikka taking over. The team, not just the Core Team, was much the same earlier when the Company was doing great and when things began to slip quite badly.
Whether one likes it or not, 'continuance commitment' creeps in over a period of time in any and every Organization, big or small, and all over the Globe.
I recollect your postings regarding PMS in many threads, and I think that's where regular review/revamp of PMS, which too I think you had mentioned in a few threads, becomes important.
Ideally, employees with 'continuance commitment' shouldn't be allowed to exist at all, but in reality, ignoring (the Best-Case-Scenario) or firing (the Worst-Case-Scenario) such employees becomes too tough from the HR angle, at the individual HR Person's level.
At the end of the day, it's quite easy to say things like 'ignore/fire them' from the sidelines, but as you know, it's extremely tough for those handling such situations at the spot.
And that's where the HR person's role becomes so very important, handling such situations with the needed finesse and win-win strategy under stressful/tricky conditions.
Regards, TS