I think they term it that way for 2 reasons: first, to try and build some fake loyalty and familiarity (you're already exclusive!) but secondly it's so their normal rate is the same as other booking agents - they can offer it cheaper by making it "member exclusive"
With regards to flexible / cancellable that's usually exactly what flexible means - you can cancel it (and as a flow on, can change the dates, since worst case you can just cancel and re book)
Extra guest charge is most common with a rate that includes breakfast and lastly I've always assumed those double points rates are a cheap way to abuse people booking business expenses.
Hope that helps...
Edit: this is in Europe though
"I SEE IT ONLINE FOR $50 LESS ONLINE, YOU HAVE TO MAKE IT CHEAPER!!!" seems to be the classic style of negotiating car prices. It seems to be the only bargaining chip that you have available to you.
The long and short of it: you're trying to win over another human being to be on your side. You don't demand that a company or "lowly employee" meet your expectations. Tact for the win!
Tried to book a one of Starwood Preferred Guest hotel. Had to create an account, but this is a given. For a single room there are 12 offers you can choose, really simple /s.
The cheapest offer is for "SPG Member Exclusive. Am I one? How do I know? I guess I'm not, just created an account, but let's try anyway since it isn't disabled. First thing they try to upsell me on a room with 3X price. Can skip it. Now the price is different, it includes VAT. Why would you not include VAT in the first place? You have to pay taxes in Europe. Ok, apparently the price includes 5% discount and a free wifi (wow). Let's try others since 5% is not that much.
Oh, if you click the small link you can see the prices without the upselling attempt. Again no VAT included, but why is this "Save 10 percent - prepaid rate" somehow more expensive then the 5% discounted rate? Maybe this is for non-exclusive people.
On the first sight "Weekend package" offer is just more expensive, no value added. Unlike other offers it doesn't say this in the title, but it includes breakfast.
There is "SPG Member Exclusive: Flexible rate". Still don't know if I'm exclusive enough, but the rate itself isn't flexible (I blame bad translation though, part of the interface is in my language, part is in English). It's just a cancellable offer.
There's also a cancellable offer for non-exclusives such as myself.
Other offers either include breakfast or are some expensive packages.
I have given up, since I don't know if I'm an Exclusive Member. The price on booking.com is the same as non-exclusive one, so really no point in booking here.
Other strange thing for me. Every place on the site mentions some points. Is this an American thing? If you just want to book a room it feels like you are paying a premium, so the points-people can pay less. How I guess it works: you choose more expensive hotel/room to defraud your employer, so you can get more points to use on your own travels. Just a wild guess though.
IHG.com hotel was no better. Again confusing pricing, where what you see first is never the end price. If you choose breakfast, it changes rate but also includes some "Additional guest charge" (???). There's "IHG® Rewards Club Advance Purchase" and also "IHG® Rewards Club" and normal rate. Don't know which can I take.
The 'points' thing here is even more ridiculous - you can pay more to get more points, like pay X more per night and get Y more points.
In the end I booked on booking.com. It was 3.65% cheaper through the hotel chain site if I'm exclusive enough (still don't know). I probably lost some points, but I don't want to be constrained in my travels with some loyalty programs. SPG only has 7 hotels in my country and IHG has 5, so I would have a hard time earning those points. Also I almost always travel privately so can't defraud my employer for points.