Hey,
if you use an appropriate licence modell (like the GPL), you wouldn't allow MS or whatever to steal youre code legaly ! OpenSource doesnt mean take it and sell it, thats not allowed with licences like the GPL. I expect you would neither bee torn away from youre programme, you could still bei the project maintainers, and you would get patches from time to time by some good programmers that had a look and fixed a bug or added some nifty feature... If you knew e.g. how Linux Thorvalds handled the Kerneltree his "baby", he was very restrictive, being the maintainer and everything, he made the major decissions on what would make it into the kernel and what would not - and this is speaking of a much much bigger project than TS will ever be (so you will have to "fear" much less coders wanting to help you).
All together I would say youre objection towards open source are mostly founded on lack of profund knowlege on the subject, and dont realy hit the point.
The advantages of open source would be clear:
a) From time to time you would recieve a patch of some friedly people that found+fixed a nasty bug (I just remember the diconnect issue).
b) coders could do some "experimenting" on the cause of the problem, which would help in giving you guys better bugreports.
c) youre image, userbase, and especially _experienced_ userbase would increase dramaticly. (Meaning better and quicker, more to the point bugreports)
d) I would love you twice as much

e) TS could be ported to some platforms (like PPC, alpha, sparc, FreeBSD, Solaris, Irix and others), which would be to much trouble for you guys, but for some PPC freak-hacker it would be some fun !
...[there surely more

]
pwk.linuxfan
PS: How about an experiment ? Make TS-1 Open Source, you cant loose much there, as TS-2 is a complete re-write right ?