The question is how long can one stay with the old bios. In 1.03a there is support for newer video memory, from there on upto 1.08 there have been some changes such as resume / startup time reduced by 1 sec, remote bios update etc.. which might not be of significance to everyone.
In future there might be a critical update, which might be related to the temperature control, or the embedded controller update might need a minumum level of bios. We cannot always stay downgraded.
Even when you buy the exact same drive model, but with different firmware version ( OEM, APPLE, DELL etc..) it doesnot work. Now it would be foolish on part of the manufacturer to sell inferior hard drives or have a different manufacturing process, just because they are being sold in the OEM channel when compared to a specific vendor like IBM. The costs involved in running two different manufacturing process is huge when compared to the profits by such a decision.
If the firmware version from IBM / Lenevo consists of "significant" improvements over the stock / generic manufacturer firmware, may be they should patent it , and charge royalty for it from the manufacturer if they decide to use it.
The keyword being "siginificant" , which i guess most of the users are not noticing when they use other drives. Or they should give out details and explain the logic and advantages of using thier high priced drives. If they have good reason, i am sure sensible people will stick to it.
Most of the people here are loyal to IBM brand because of the quality, if they let people use other disks and if the firmware makes such a difference, i am sure many people here would not mind paying a higher price for the quality. Since that is not happening, someone decided to resort to cheap tricks like having a whitelist even for hard disks.
It is an entirely different thing to protect intellectual property ( TCPA, product activation, licensing etc..) and limiting customer choice.
As seen in many comments, the T43's are running hotter. The quality of the NMB/Thai keyboards is not same as earlier ( I have 2 keyboards with same FRU , but entirely different finish / quality ).
The quality is still not as bad or lower when compared to others, but i have seen 2 people whom i know, recently switched to dell because of the following
a) the heat seemed to be comparable to them between a T43 and D610
b) the ability to upgrade the cd drive to a much better dvd writers ( 9.5 vs 12.7 ) , regular connector vs a special connector
c) huge discount coupons, screens are comparable, similar wireless options, identical hard drive capacities and graphics options.
If the intention of this firmware check was just to keep the customer informed then this is implemented in a bad way, unless they cover all possible firmware levels in the database and have a genuine need to be above a certain level.
The whole idea of free societies, IBM advertising its linux initiative,open markets, promoting democracy, spending billions of dollars on wars, seems like against this hard disk whitelisting to contol the freedom.
Who knows may be the chinese government with its stake in Lenevo wants to control world hard disk market ( == controlling free speech / democracy in china ? )

, just kidding !