Well, each individual guitar has it's own tone... even if its very similar to another one of it's model, though not every guitar can be made EXACTLY the same as the last...

Tambre? Well, Ive seen it with an i and an a... eseetially meaning the same thing... though I have always known it as the way the player PRESENTs the note, not the tone of the axe ITSELF....

Why cant you learn modes and so on a great guitar? Well, there is certainly no reason why you cant, or shouldnt...though I always did. What if you always play with great, really smooth working necks, set up nice and such.... but to one day break out of the norm and play with a crappy guitar? You might not have the strength to play it without screwing up. If you learn it on a horrible guitar, and play it whenever you may on a great guitar, your not at a disadvantage when playing a high quality axe. Alas... opinions aperantly seem to vary with person to person....

Knowingly buying a crap axe... well, first off, if you knew you were buying one, you would know what to look for, such as a truss tod... though Martin didnt put ones in thier guitars for a while, though Martin makes some niiiiiice guitars. Plus, you would also probably know how much to pay for it at THE LEAST, not being ripped off by some cheap salesman... There is no reason for not having a great axe with a great set up, unless for lack of funds in your pocket, or whatever the reason may be...