Does full range guarantee bass?

Equipment cannot gaurantee sub-50Hz bass. The key determinate of high quality deep bass is the interaction between your room and your speakers. Speaker/listener positioning is critical as well as appropriate equipment isolation from feedback. Somewhat paradoxically, subwoofers work best with those speakers that need them least. I take the position that subwoofers shouldn't be used to provide bass, but are only appropriate for deep bass (sub 40Hz) augmentation. REL subwoofers are a good embodiment of this line of thought.

As far as amps go, some amps have slightly different deep bass qualities, but these differences are not comparable to the influence of room acoustics.

The Vandersteen subwoofers (2Wq and V2W) are meant to be used with full-range speakers due to the contour (slope) of the crossover. The Vandy subs cross over at 80Hz, using a more gradual slope (I can't remember if it's a first order or second order filter, but I think the latter). Hence, there needs to a full octave overlap, covering the 40-80Hz range, for the Vandy subs to blend seamlessly with the main speakers.

Where to begin? First of all, "full range" means nothing. It's advertising copy. Buyer beware. (All right, when a-philes use the term, they DO mean something close to 20-20kHz. But any manufacturer can call any speaker in its line "full range.")

Marakanetz is right that many speakers can indeed produce some very low bass output. What matters is whether it's flat, vis-a-vis the midrange. And Onhwy61 is right about speaker-room interaction.

Pairing what we might call a "reasonably full range" speaker with a subwoofer can be advantageous, since you have more flexibility on the crossover.

As for amps, they cannot put back what a speaker takes away. (If they do, I'd suggest finding another amp.) Going in the other direction, if a tube amp is rolling off the low end, adding a sub and cranking it up (or tweaking an equalizer, which amounts to the same thing) will give you more bass, but not generally the kind of more you want.

If you like the sound of a tube amp that rolls off the bass, then trying to put back the bass makes no sense. If you want full-range sound, you need both a full-range amp (which includes many tube amps and most SS amps) and a full-range speaker system--which means either a large speaker with a large driver (or combination of drivers) or a sub.

Vandersteen's 2Wq is a 6db slope. It operates below resonance and requires a main speaker that will perform down to about 40Hz for seemless crossover. Also, one of the benefits of the Vandersteen subs is the insertion of the 6db crossover filter in the main amp signal path. By reducing the load on the main speakers, you get better dynamics, bettter transient response, transparency and definition from them. It is an interesting system to say the least and one that I use and believe in.
Richard Hardesty stated that you cannot place a full range speaker in any one position that will give best bass performance and best performance through the mids and highs. Something I have learned from experience. He also agrees with the Vandersteen system for best performance.
With all that said, it should be obvious that just because a speaker is full range, it doesn't mean it will give you accurate sound(something that seems to have gone out the door in recent times-but that's for another day)and bass response. A speakers enviroment has more to do with the sound than any other component. Bad room, bad sound.
It does mean the speaker will respond to an input signal at its lower frequency limits. It doesn't promise it might not consist primarily of harmonics and distortion. You don't see many speaker manufacturers talking about distortion in their speaker. Most speakers are well over 10% distortion (actually pretty good systems)at even low drive levels in the bass. Some are a lot higher than that.
As you can see, the answer to your question is a big---depends!

It depends on a number of factors.Room interaction is very important.You can get great Bass from 2-ways that amazes me. Amps also need to be matched with the speakers to get the peformance out of them.

Others here have brought up some very good points.