yeah most of the big ISPs will have extensively tested whatever they provide, as believe it or not, they dont want to spend millions of pounds on helpdesk calls each year
BT have their own stuff built, other manufacturers have to pay a few grand to testin BT labs, which a small number still do, just to ensure things actually work ok.
Other ISPs will have a "supported list" of modems/routers i.e. their staff have tested them and said they are "ok"
buying a cheap modem router and wacking it on your ISPs network is just pot luck ...Netgear have a very good rep, the DG834G being (i think) the biggest selling individual modem router in the world (thats not given away) i.e. the one that most people choose to buy - probably over 5 million in use in the UK alone (another reason why you see 'more' people with issues ..because theres not 100K units out there in the UK...theres 5 million)
I havnt played with the v5 of it, im guessing it has the latest Broadcom chipset.
Thats another thing, theres only 3 decent chipset vendors IMO - the big boys are Broadcom,Texas Instruments and Conexant all of which have deployments in the hundreds of millions worldwide at both ends of the copper loop.
All the manufacturers are dependant on these guys testing their new chips/drivers with the others...can you imagine how many DSLAMs, line cards and software versions there are deployed around the world...countless.
So basically you are reliant on how much lab time, at the chipset vendor, manufacturer, public beta, and service provider stages have been undertaken...get some rushed out code to fix "issue a in country b" and it can mess up "country b" performance etc etc and so it goes on
to summarise, when you get some good performing firmware for your product, on your line/ISP ...stick with it, unless you have a problem that specifically is fixed by some new stuff ...if it aint broke dont fix it !