Storage & sms trouble.

NB. I would have posted this to an HTC Desire forum, but you don't seem to have one, so I hope the following isn't out of place here.
Hello. I've tried asking what I think are a couple of simple to ask tho not necessarily simple to answer questions on a few other android device/app forums, but for some reason the feedback has been less than helpful, or even non existant; this site has been strongly recommended to me by a friend, so here's hoping. I have an HTC Desire with a 16gb micro SD card, and 14.6mb free on my internal storage, and I transfer and/or save all apps and downloads to the SD card. My first question is, is it normal that although I have free space on my internal storage and save all downloads to my SD card, and only keep very small apps on my my built in storage, the 'warning low space' icon is permanently lodged on my menu bar, and even though I try deleting apps stored internally it never disappears? Maybe I'm stupid but surely storing items on the sd card should not result in my internal storage running out of space. On a pc this wouldn't happen, so why does it on a smartphone. Is there anything I'm missing or can do to rectify this situation? Secondly, for some reason, when I write a long sms msg on the HTC message widget, I get an on-screen alert telling me the msg is being changed to an mms, and then to an sms and then to mms and then sms ad Infinitum. Any ideas why this is happening and what can be done about it? Finally, how would one go about adding a town to the weather widget if it isn't listed/can't be found within the application? I would gratefully accept any help, ideas, advice or information you could give. Many thanks in advance. J.

Thank you so much for your response Steven, in one simple reply you've given me more useful advice and suggestions than all those I received on 3 other android user forums put together. To answer your questions, firstly no, I am far from comfortable rooting my phone, although knowing it's not just me who has had this issue does relieve me slightly, for I thought that maybe I had created a software conflict or that invisible, redundant files were clogging my device as is common on pc's et al. At least on the last point I was close, sadly tho a smartphone system cleaner and/or defragger doesn't appear to be as readily available or effective (I have used and had too many problems with Symentec Norton in the past to consider using it again on a pc, I have had good reports of it on smartphones. Would you agree with that and do you think it'd help me at all?). I have considered rooting esp' in light of the fact that a pal of mine used a one-click app to do it and so far has had no problems with the result; however, I am not in a financial position to take the risk, and have absolutely no real hacking experience. I used resedit extensively on on Mac's in the past, but when it comes to code and smartphones I am about as competent as a blind man on an obstacle course. I would seriously think about using a one-click app, but only if I knew someone near to me who could advise and oversee what I'm doing. You have settled my mind about it being my 'fault', so many thanks for that. Secondly, I have backed up and performed factory rests twice, each time resulting in a nice clean, fast machine, and each time ending up with the same problem. At least I know why now. Yes, I regularly clear my caches. As to contacts, I have 147, so not really thousands; would deleting a few help, as I've a second handset that has a copy of all my contacts on it, so I could lose a good few maybe? Finally, the weather widget I'm unable to add cities and places to is the one that came pre-installed on my 'phone. Is there a 'better' one out there or is there a way around my problem that I'm unaware of? I think that cover's it, so anything you have to say in reply would, as ever, be most gratefully received. Thank you again. J.