Perhaps it is because I am also a U2 fan, but honestly, I do not get the reference. I really don't (I don't see it in "To Live Forever", either). Maybe it's the inspiration, but I don't hear very much U2 in any of DT's work, to be honest. Perhaps it's because I think The Edge is a pretty singular guitar player, and I don't hear much of that in Petrucci's work.
I don't consider myself a fan, but I've listened to most of the band's albums (all of them except for
Zooropa and
No Line On The Horizon), and I think the comparison to U2 might be because:
1. The choruses sound similar to the ones in "Where The Streets Have No Name": they are big / anthemic / uplifting, both are in D major, and there's even this simple melody (the notes are A - G - F# - D) present throughout - in "IWBY" it's played by the keys and guitar, and in "WTSTHNN" it's played by the guitar and with Bono singing 'burning down love'. (Both choruses also share the same chords, albeit in different orders).
2. As for the verses, they remind me of "City Of Blinding Lights", which -as you surely know- came out in November 2004, when Dream Theater were beginning to work on
Octavarium. Mike has stated U2 is a band he listens to and takes ideas from, so maybe he liked the
Atomic Bomb album and immediately decided to pay tribute to the band.
3. Overall, the guitar parts in "I Walk Beside You" are really simple, with nothing too flashy, sometimes playing repeating patterns in just two strings (like the riff in the intro and verses). That, obviously, reminds of Dave a lot. The bass parts are steady and simple too (mainly playing roots and eighth notes), and the bass is prominently featured in the mix, and both things remind me of Adam a lot (especially in
Boy and
War). I don't remember reading statements by either John praising Dave or Adam, though, so maybe Mike made suggestions on the style of the song.
As for "To Live Forever", there is some guitar bits with delay (like at 1:35 and the outro), so there is an influence there. Also, I don't know if it has to do with reverb or what (I'm not very good on audio terms), but in the first half of the song - before the heavy guitars come in - there is a strong '80s vibe a la
The Unforgettable Fire.
I also think there is a strong U2 influence in "Lifting Shadows Off A Dream", with the guitar playing short, repeating patterns with delay, and some open strings. The choruses (the last one at 4:50 especially), once again, are similar to "When The Streets Have No Name" - anthemic, in the same key, sharing the chord progression, the A-G-F# melodyy, the guitar with delay...
The same with "Take Away My Pain" - the guitar sound in the verse reminds me of the rhythm guitar in "One Tree Hill".
(By the way, how come there's not much U2 talk in this forum? Guess we should start a U2 thread)