Good observation.This is something I have noticed as well. This is how I see it:
Cash offers: Yes, these are the lowest offers. Usually, made on distressed properties and might need some rehab. 70% ARV- Repairs/Closing costs = Offer price
Bank Financing: The home would have to be in really good shape to use traditional financing, so this will usually be right around the full value of the home.
Seller Financing: This allows investors room to get creative. The offer price can be right around 70% ARV depending on the condition of the home. Use the 1% or 2% for rents (assuming this is a rental). If it cash flows well you can sell it as a turnkey to another investor or as personal home using seller financing at the ARV. Making enough to get your original investment back (the down payment and light rehab), pay the original seller every month, and some cash flow for yourself.
I hope this helps see the picture some. I don't have a perfect calculation, but from my understanding, this is how the deal is structured. A lot of this depends on what kind of deal it is. E.g. buy and hold vs fix n flip vs short sale etc.