Problem is, if 4e is your first D&D game, you pretty much have no clues on how to do it apart from "everything has to be balanced or Something Horrible will happen and you'll stop having fun". If you grew up reading Gygax articles, you already have all the baggage needed to bring "old school" to any game (Heck, I've even run Gygaxian Risus), but if you're just stretching your DM wings and don't know any other advice than the 4e DMG's, it seems like your only option is to purchase correctly balanced monster groups and locating treasure parcels of the right level.
I'm really, really, really trying to see what's bad with that. Now, the 4e DMG doesn't say "every encounter should be average difficulty" and, indeed, has some quite difficult encounter set-ups (hard encounters are hard in 4e), but for a beginning DM, surely you want a game that is enjoyable for those involved?
What did Gary say in the AD&D DMG? Oh, yes:
"AD&D means to set right both extremes. Neither the giveaway game nor the certain death campaign will be lauded here. In point of fact, DMs who attempt to run such affairs will be drumming themselves out of the ranks of AD&D entirely. ADVANCED DUNGEONS & DRAGONS aims at providing not only the best possible adventure game but also the best possible refereeing of such campaigns." (DMG page 92).
Both 3e and 4e have come closer to that in terms of providing a framework that gives a range of encounters from easy to extremely difficult, and treasure to match, which aids the beginning DM enormously.
Cheers!