Do we really need anything more than 8" woofer and 1" tweeter for medium size room?

This is a very good question indeed. I think it all depends on the type of speaker, the room and what you want to use it for. To answer the question, i think it might be all you need. It depends on the speaker you buy. I have a pair of Wilson audio Duette series 1 speakers that can be very bassy depending on where they are in the room. They dont have sub bass but quality bass. I use them for both music and movies ( just 2 channel no surround sound) in my room and im happy. The room is a bedroom though so that might not qualify as a medium sized room though. It all depends on how far back and how close the speakers are to the side walls. Too far back and far apart they can be boomy!! But bring them out into the room and put them closer together then they will have good bass but not boomy and airy treble with 3d imaging. Thats perfect for music! For movies yea a sub could help out for shure but i dont feel the need to buy a sub. They have an 8 inch woofer and 1 inch soft dome tweeter. The sensitivity rating is 89db. 4ohm speakers. Now lets say they had a 10 inch woofer. That extra 2 inches might make them 6 db’s louder and thats alot! but yes deeper too. I dont want them to be any louder then they are because they are very loud lol. Do i think all speakers with an 8 inch woofer can go as deep as the wilsons? no because of the design of the cabinet, the woofers they use and the crossover design. So listen before you buy. A more affordable speaker with a 10 inch woofer might do what these are doing with an 8 so who knows lol. Also everything matters. The equipment they are connected to can make a difference so choose wisely.

Again, I think it depends on the type of music you normally listen to.  If you came over and sat in front of my system with the Tektons and REL G1 and I played you some Muse and Volbeat at loud levels, then you transport back to your system with what you think is "full range" sound and listen to the same tracks, it wouldn't even be close to the same experience... just not possible.  But that type of music may not be your cup of tea either, which I understand.

If I always only listened to Norah Jones, Mary Black, James Taylor, Michael Buble, etc., then my system would be totally different.

Yes - I not talking about HT movie watching bass or heavy rock bass - just jazz, blues, country, classical, r&b, acoustic bass.

I really don't want my floors and walls to shake - just the sound of a live upright bass, or bass guitar, or live drum kit, etc. - which is what I've got.

There may be no right or wrong answer here.  Everyone makes a good case for their preference.  I have 6.5" full range drivers (SET powered), crossed over to super tweeters at 10k and an 8" sub.   I don't need anything more than the 8" sub.  Within the limitations of the system and room (garage) it has plenty of oomph.  In another system I have speakers with 10" drivers.  I don't need more.  I tried a 12" sub and could plainly hear it down the hall but not at all in the room itself.   But an 8" driver wouldn't be satisfying in that room with my taste in music.  So within the confines of that system and room 10" is optimal.  If I had a dedicated room with full treatments and optimal dimensions I think I would want and need 12" drivers because they are so much fun..  

All this talk of high end 10 and 20 thousand dollar speakers , backed up with this sub or that sub, maybe you should be looking back instead of forward.
There are plenty of great vintage speakers out there that will sit you back a fraction of what is being discussed here and do an excellent job.
For a really great speaker, that's off the radar find a pair of Time Frame 600's, very nice speakers and they have the small drivers.
Find a pair of used Bozak 4000 b symphony's, super speakers.
I am a big Altec fan and nothing moves air like a 15 inch driver topped with a nice Horn on  for the mids.
I build my own speakers now, I have a pair of Altec model 19's I built of my own design, using GPA 416 drivers , GPA model 19 crossovers and original 811 horns with 802 drivers.
They have super clean , fast bass and will make you think an orchestra is in the same room with you.
They will literally shake my 3600 sq. ft. ranch home with clean  low end bass and  clean mids, no need for subs.
They did not cost 10's of thousands of dollars and did not need to be built in some super fancy boutique speaker shop.
Simple designs with good quality components and yes Great Plains Audio is the Altec of old, just a name change.
I would put these speakers up against any 25000.00 speaker and not flinch, the finish would not be as nice but I don't look at them, I listen to them.
Well maybe I do hug them once in a while, they are over five foot tall and 32 inches wide.