Well, after a little bit of online research, I think I know what it means. A "power creep" is usually used with relation to the Trading Card Game, but it basically means that things in the newest generation are more powerful than those in previous generations.
This can be seen in several ways: firstly take Persian and Ambipom. This is a pretty basic example I made up myself, but there are undoubtedly more powerful versions of it around.
Persian was introduced in Gen I, and Ambipom in Gen IV, so take a look at their base stats. Ambipom is higher in EVERY SINGLE STAT, with the exception of a tie in speed, and Persian has 5 higher in Special Attack (whoop-dee-doo - neither Pokemon should use that stat anyway). So is there absolutely any reason to reason to use Persian over Ambipom? Not unless you really like Persian's design more. Well, OK, competitively this is why tiers exist. In the Black/White tiers (since we don't know the Gen VI ones) Ambipom is UU while Persian is NU.
A lot of Pokemon show this trend, with Gen I Pokemon (in general) being a little weaker than their later generation counterparts. If you go through and count how many Gen I Pokemon are still in the OU tier, there is only about 10, many of which are only there thanks to changes made in BW (e.g. Venusaur got the ability Cholorphyll, and Cloyster got access to Shell Smash, both of which was simply overpowered in the lower tiers).
This brings me to another point. Power creeps are not about looking at the stats of the new Pokemon. New moves and other new mechanics also play a part. For example, look at the stat boosting moves. Before Gen V, every single stat boosting move never gave more than a net +2 to a Pokemon's stats, with the exception of Belly Drum, but since that halves the health of the user it was hardly ever used anyway, and Amnesia in Gen I only (which was completely overpowered, but changed thanks to the splitting of the Special stat in Gen II). Aside from these exceptions, everything gave a net boost of +2 at most. Now take a look at Gen V. Tail Glow was changed so it gave a +3 boost to Special Attack (Prankster Volbeat with Tail Glow and Baton Pass can be a nightmare to anyone unprepared for it). Shell Smash was also introduced, and completely blew the above rule out of the water. +2 to Attack, Special Attack, and Speed, and
-1 to Defence and Special Defence = a net boost of +4. If the user is holding a White Herb the lowered Defences are negated, giving it a literal +6 boost, with absolutely no drawback. So much for a max of +2.
So, in short, "power creep" is simply a way of saying that with many new generations the Pokemon get stronger, so threats from earlier meta games can seem less powerful in the current meta game, and there are new things to watch out for. In relation to Scizor, it could stay in OU, simply because the tier in general would get more powerful. Lucario is also a good one for Fairy-killing, although it lacks Scizor's resistance to them, and Venusaur and Gengar are potentially other good choices against Fairies. Many of the dragons might also drop a tier (possibly) because they might be completely walled if the opponent sent out an Igglybuff (OK, maybe not an Igglybuff, but you get my point).
Well, I hope my rambling made some limited sense.
Some of my examples are also from that page, but some I kinda made up, but they still work.