No, they wouldn't -- a reader or solo chanter can do the responses in the absence of a full choir. In the Byzantine tradition, this became fairly common during the Ottoman era, since the training of full choirs was very difficult. The association of Byzantine chant with solo psalti grew out of this, but the tradition of Byzantine chant sung by choirs (very beautiful, and by necessity, very un-ornamented) is making a strong come-back.
As to the memorization of variable material, this really only occurs for the troparia and kontakia of the Octoechos on Sundays (they repeat every 8 weeks), and for troparia and kontakia of festal seasons, since these are repeated many times during the services of the feast and during the post-festal season. Some of the Resurrectional stichera for Vespers from the Octoechos becomes memorized by those who attend Vespers regularly, but this is less common.
On a given day, between Vespers, Matins, and Liturgy, there are usually 4 - 8 folio-sized pages of closely spaced text that contain the variable material. This obviously would be very difficult to memorize, even for chanters who were in a monastic setting.
This, incidentally is why Eastern-tradition parishes that claim that the congregation sings "everything" are usually not telling the whole story. In most parishes where this is supposedly the case, the real story is that only Liturgy is being served, and not the other services -- and/or large amounts of variable material are being omitted. It is virtually impossible to do the services with completeness without much of the material being done either by a choir, solo chanters, or both.
In any event, God willing, traditional Western chant will make a comeback in the Catholic church. Most of the Gregorian chant recordings that I have are very sterile and academic -- hardly chants that people could learn and memorize, and it seems that the continuous living tradition of Western chant has been largely broken. Are you aware of recordings that have the kind of simpler Gregorian chant that congregations could sing? And what about in English? (And here's the "hard to please" part -- good English?...)
Some of us are trying very hard for this.
Most of the Gregorian chant recordings that I have are very sterile and academic -- hardly chants that people could learn and memorize, and it seems that the continuous living tradition of Western chant has been largely broken.
I quite agree. Most of them are focused on over elaborate vocalizations of the proper chants of various Masses.
Are you aware of recordings that have the kind of simpler Gregorian chant that congregations could sing?
Well, if you can find one for an ordinary of the Mass in plainchant, it should have it. All to frequently though, these type of recordings have some outlandish concert hall style music from Mozart or some such, and completely ethereal proper tones. Otherwise, you would need to visit somewhere it still lives, such as St. Boniface Church in Pittsburgh, Corpus Christi in New York City, or Most Holy Family Monastery in Harvard, MA.
And what about in English? (And here's the "hard to please" part -- good English?...)
For this, you are best off looking around at what the more liturgically correct Anglo-Catholics have to offer. They also have some beautiful Elizabethan Polyphony. I have one I love called "All the Vales Rejoice" put out by the Choir of St. Mary's of the Hills (Episcopal), but recorded in St. John's Church (Episcopal) in Valle Crucis, NC.
Your best bet might be visiting one of the Churches listed on the "Forward in Faith" website and seeing what they can steer you towards.