Life was simpler when I thought it was just a simple resistor pull-up. I just read the details in my Atmel datasheet and see the issue.
for 'classical' derivatives "the bible" is a much better resource. Now, beware, many moderm derivatives have multiple modes for the ports (I recall none where the defsult is not "classical") susch as push-pull, input (as you describe below for the PIC), analog, open collector/drain, .....

I had been working with Microchip products that give a true high impedance input so you can do things like directly connect to the powerline via several Megaohms; it is taking me a while to get a handle on the 8051 features.
Today, more or less, if there is a 'feature' you do not like, there will be a derivative where that 'feature' can be modified to your liking. If you look at e.g. the SILabs deviates (f3x-up) you will find the, for all practical purposes, everything except the instruction set is totally different from the 'classical' '51..

Erik

here are the links to "the bible"
Chapter 1 - 80C51 Family Architecture:
http://www.nxp.com/acrobat_d...ARCH_1.pdf

Chapter 2 - 80C51 Family Programmer’s Guide and Instruction Set:
http://www.nxp.com/acrobat_d...UIDE_1.pdf

Chapter 3 - 80C51 Family Hardware Description:
http://www.nxp.com/acrobat_d...WARE_1.pdf