Zack
It's not that there is a problem. All the pentax scopes have a pin down at the bottom of their 1.25 eyepiece recepticle that lines up with a slot on their eyepieces. When one takes an eyepiece made by someone else it only goes down as far as this pin and hence keeps the eyepiece about 1-2mm further out and can affect the available range of focus with that eyepiece. This is not a problem because it usually can be handled in one of two ways. The first is that if the barrel of the eyepiece is long enough one can create a slot in the eyepiece barrel to accomodate the pin. If the eyepiece barrel is already short one can install a telenegative lense in the bottom eyepiece threads which effectively changes the focus range and slightly increases the eyepiece magnification. Take for instance I have the scopetronix WA18 lense and for the pentax this eyepiece requires a scopetronix maxpower lense to be installed.
Probably in true fairness I would probably suspect that the pentax system may offer the widest range of possible eyepieces availility to use third party eyepieces. I have absolutely no regrets for my purchase or selection. Actually I feel I've got possibly one of the best situations available due to fact that I can pick and choose the combination which is best suited for the purpose I have in mind. If I'm bird watching with this scope or decide to star gaze with it at night, I can change my eyepiece to best suit the purpose of choice at the time. Take for example my brief try of the speers waler10mm, If a problem does present itself I'm pretty sure that one of the two stated options should allow a usable situation. Not every eyepiece will have a problem. The same can be said with any other scope that can adapt 1.25inch eyepieces to their scope. Some will work others will not and chances are the available focus range will be the affected concern besides quality of image, eye relief, field of view, etc.
With spotting scopes I am really coming to the opinion that what really sets one out from another has a lot to do with the quality of the eyepiece alone. Granted there is the much to do with the type of glass and placement in the scope that can affect the image quality. However if you take two scopes that have quality Extra Low Dispersion (ED) optics installed, the most probably difference in image quality will probably be with optical quality of the eyepiece.
I again iterate that I have no regrets of any which my choice on this scope, even though I had a couple of trials and tribulations during the aquisition and availability. If you are thinking of image quality and brightness and I would have no reservation in suggesting you go with the 80 or even the 100mm scope. I accept the tradeoff of image quality at 60x on the 65mm as compared to 60x on the 80mm scope. Personal view point is the image is slightly softer. Again I think most of this is attributed to the zoom eyepieces.
I hope this helps to clarify the situation. I would recommend that you try your prospective scopes out if you can and make the choice based on what your willing to accept. It might be cost, form factor, weight, versitility, ultimate clarity, all depend on your intended usage. If you go with pentax or any other that can accept astro eyepieces I would suggest as someone else in another form has done and that is to go down to an astronomy store and try every eyepiece they had in the store with your scope. You will find what works and what does not. You have to remember some of these eyepieces can cost as much or more than the scope for the high quality eyepieces.
Todd benko