I think there is some confusion over what exactly series links are and what they should do
They are not a given on SKY digital for a start nor are they under the control of SKY or do you pay for them in any form what so ever.
Series linking is the responsibility of each individual broadcaster and the ability to implement series links on their programming is one of the facilities of the EPG which they pay SKY to use.
If a series link exists yet doesn't point to the next episode correctly then the data that sets up the link is wrong and it's either become corrupted or more likely carelessly set up by the broadcaster in the first place.
Some broadcasters choose not to support series links at all, I suppose it saves them a few quid a year by not employing someone to compile the relevant EPG data and send the information along with it's EPG listings.
Comparing series links to the TIVO equivalent is a bit pointless since the series link system is all that is left for SKY to use as TIVO patented virtually everything to do with PVR software and methodology. SKY for obvious reasons choose not to license the TIVO OS which works so well because it's basically the US service and the US subscribers would not put up with anything like the service levels SKY get away with. TIVO has thousands of UK subscribers paying for people to compile TV listings from all UK broadcasters, insert flags and hooks and then send that data to every TIVO user every day.
That is a far cry from the SKY series links which are the domain of each broadcaster, on the surface that should mean foolproof listings etc and no mistakes with their own programming but in reality it's just another way to offer a poor level of service and save money.